I’m a huge proponent of Easy Digital Downloads as a great way to sell products online. I think it’s the only really viable solution for WordPress plugin developers at the moment who want total control over their sales process. One of the best parts of Easy Digital Downloads is the system of first and third party extensions you can install to increase the base plugin’s functionality.
This extension system has given way to people building entire businesses inside of the Easy Digital Downloads ecosystem. One such company, Sell Comet, has released four extensions (with more on the way) and is the focus of this interview.
Sell Comet’s founder, David Sherlock, went the extra mile for this interview and gave the most thorough answers I’ve received to date. David goes into how he got started making Easy Digital Downloads extensions, how he picked the name for his business, dealing with concerns over his products being cannibalized and the thought process behind the ideas and development of each plugin he builds.
Can you tell me a bit about yourself and how you got into building extensions for Easy Digital Downloads?
From a young age I’ve always had a deep interest in computers, music, and software development. In 2010 I made the decision to leave my full-time job as a security analyst for Hewlett Packard to start my own soundware company selling sample packs and sounds for electronic music producers under the name Freshly Squeezed Samples. The site was initially built using a heavily-customized off-the-shelf PHP script, which was rather primitive at the time (it required the customers to enter a license key to download their purchases – causing a lot of confusion in comparison to sites like Beatport), but nonetheless it proved the business model worked and helped get things moving. Back in 2010 finding “scripts” for selling digital products was extremely difficult, because everything eCommerce-wise seemed catered towards physical goods and shipping, with digital downloads only initially gaining traction in the form of sites like Beatport, iTunes, and alike.
Over time, the business grew to gain a large international following, with customers including the likes of Armin van Buuren, Paul van Dyk, Aly & Fila, Above & Beyond, etc. During this period, my design and development skills also improved in tandem with the business growth. However, I had a major setback in 2015 when the EU introduced complicated new VAT rules (known now as “VAT MOSS”), which were incompatible with the way the site was originally developed to handle taxes, and effectively required a full rewrite to facilitate the new taxation rules. Furthermore, because I discovered this a little late in the game (around November, and it was due end of December), I scrambled to implement a solution in time for the new year. Because of the short notice, I had to cut some corners and broke a few things on the site including the coupon code system, which contained some tricky logic regarding how discounts work and where the “discount” was applied (it applied to the order total rather than per-cart item, so items couldn’t be excluded easily).
Because I was never really a “fan” of discount codes anyway (since it’s not fair on customers who miss out) and because our products were considered “premium”, the business has been running without them since 2015! However, I have reached a point now where I want to rebuild the site from scratch with a full brand refresh, and I personally feel that WordPress is now mature enough (alongside Easy Digital Downloads) to handle our traffic and audience.
So, because not everything I needed was available as an extension for Easy Digital Downloads, this ultimately prompted me to take matters into my own hands, get into WordPress development, and build these additional features that I needed for the new site.
I have to know: where does the name Sell Comet come from?
I originally purchased the domain with the intent to build a kind of Selfy/Gumroad marketplace where vendors could upload products and sell them through the site. Then I discovered that Pippin Williamson was building the exact same thing under the name Sell Bird! Because I didn’t want to compete directly, I decided to change the direction of my original site Freshly Themes and focus on building plugins for eCommerce stores instead of themes.
From the start I had the tagline in my head “Skyrocket your eCommerce sales”, which was going to have a little rocket icon and some kind of “planet” focus. However, the domains I wanted weren’t available at the time, so I eventually settled on “Sell Comet”, where the idea of the comet leaving “dust” behind worked well with the concept of leaving your competitors behind when using our extensions!

What are the most common difficulties when building Easy Digital Downloads extensions?
There are a few common difficulties in my mind, which would be:
- EDD already has a comprehensive marketplace of commercial plugins, with solutions to most common problems already available, so thinking up new ideas can be tricky and you need to be creative! I usually check out what type of plugins WooCommerce and Shopify have available and sometimes that can spark an idea or two. I also like to stay up to date and get ideas from sites like Product Hunt and Indie Hackers to see if any of those business models can be moulded into an extension for Easy Digital Downloads.
- As with the above, a lot of EDD stores already use a wide variety of plugins, so making sure your plugin fits well and doesn’t break any existing extension functionality can be tricky. For example I recently had to verify that my Commission Fees extension worked in tandem with AffiliateWP which also “adjusts” commission amounts based on affiliate referrals. Luckily, after some testing I managed to get both working side by side! Being aware of the plugin ecosystem (including themes) is definitely a consideration when developing extensions for the platform.
- The main thing that drew me to EDD over WooCommerce was the quality of code, lack of bloat, and the simplicity of the plugin architectures. All of the code I checked within core EDD and most of the extensions was well commented, structured, and easy to extend via action hooks and filters.
Outside of the above, EDD has an awesome boilerplate plugin that helps structure your plugin using the correct design pattern. This has proven to be a great starting point for almost all the plugins I’ve developed thus far.
I very recently spoke to Katie Keith, of Barn2 Media, about the dangers of plugins one day turning into core features of the product they are developed for.
Do you have the same concerns when building extensions for EDD and how do you deal with it?
This is actually an interesting question because one of the plugins I released recently that allows store owners to apply different tax rates to physical goods and services is planned as a core feature in the 3.0 release of EDD. This isn’t really a major concern to be honest, because most of the plugins I build are built because I need them right now (rather than later) for my own businesses.
I actually wanted to sell merchandise alongside the soundware products on Freshly Squeezed Samples, thus the physical tax rates. If other users can benefit from the functionality then that’s an added bonus! This was one of the reasons I released this specific plugin for free, knowing it would be eventually depreciated.
Also, because I have a lot of ideas for new plugins, it’s not something that I would let stop me at this stage unless EDD decided to copy my entire plugin catalog!

What goes into your thought process behind deciding what the next extension you make is going to be?
I come at this from two angles:
- Building and growing businesses is hard, really hard in fact – so it’s nice when you search Google and find plugins that solve your pain points at a low cost. My passion is to build extensions for Easy Digital Downloads so it’s possible to build ANY type of online digital business. Because EDD can be used to sell digital products and also services, it makes sense to extend it to support all types of digital businesses (in theory it could even be used to build something like Deliveroo or Just Eat!). A big part of my passion and persona in life is developing the “tools” needed to enable others to achieve their goals. Life can be tough, and if you can build something that makes it a little bit easier or happier for someone else, you should do it!
- Most of the plugins I build are out of my desire to test new business ideas and I build them in such a way that they can be released commercially with some customization options. On that note, I like it when software has “just enough” options but isn’t overwhelming to the user. Most of the time when customers buy a plugin they are looking for the difficult decisions to be made already with the software well thought-out to handle pain points.
How do you go about marketing your extensions? Do your free extensions tend to lead people into buying your paid ones or have you noticed other ways people are finding your products?
I originally launched under the name Freshly Themes with the intention of releasing only WordPress marketplace themes for digital stores. However, I noticed that a lot of the functionality I wanted to add to the themes was more suitable for plugins. In the end, I eventually ended up releasing only free plugins for EDD, which were relatively popular (averaging around 3-5 downloads per day, excluding WordPress.org downloads). My passion is more in providing “solutions” than theme design so plugins felt like the right way to go. At the minute I get some traffic from WordPress.org, but the majority comes from the Easy Digital Downloads 3rd party plugin page. Once I release some bigger commercial plugins I am going to look more into running Google ads and maybe even Facebook.
As an interesting side note, I find that posting “daily tips” for your audience/customers can be a great way to offer value and build genuine brand support. For example a tip could be something like “Use the commissions plugin to set aside 20% tax to a dedicated ‘tax’ user to help keep better track of your store earnings versus tax due at the end of the year.”

I ask everyone this: what’s one thing you wish you knew before you got started with Sell Comet?
I have gone back and forth a lot on thinking I should be developing for WooCommerce because the audience and potential customer reach is bigger. EDD is fantastic software but the audience reach isn’t as big as something like WooCommerce, making it harder for your name and software to get noticed. This is probably due to the fact that people tend to be involved more in drop shipping, physical goods, etc.
However, EDD is easy to work with and the code is generally a lot cleaner than other platforms, making the actual programming process a lot more enjoyable – and I need to enjoy my job!
Regardless, for one of my forthcoming plugins (Persistent Audio Player) I am building it in such a way that a version will be released for EDD and also WooCommerce, although probably not at the same time. Since the core functionality is very much native to WordPress, it makes sense to do this. With that said, specific integrations are being incorporated for Easy Digital Downloads – Frontend Submissions so vendors can also upload audio.
What’s next for Sell Comet? Are there more extensions on the way you can talk about or preview a bit?
Being honest, I have a huge list of ideas and a few bigger plugins in development at the minute! Here are some details about the main ones that are currently in progress:
- Because I sell audio files, the sites I build need to have a really good audio player. Sadly, everything that exists for WordPress is either an on-page player or only supports a single playlist. Because I actually need this, I am currently developing a persistent audio player that allows each product to have its own individual playlist. The tracks are dynamically added to a ‘sticky’ player playlist at the bottom of the screen, functioning the same as Spotify, SoundCloud, etc. This player will be called “Persistent Audio Player” and initially released for EDD with WooCommerce planned for the first quarter of 2018. It’s lightweight and built on mediaelement.js, making it a great solution for building scalable audio-based marketplaces.
- Every script or plugin that exists for launching a “service” marketplace like Fiverr or Envato Studio has been pretty much useless or extremely bloated so I am building a complete service marketplace solution that integrates with Easy Digital Downloads Frontend Submissions and Commissions to allow you to build any type of service marketplace. This will feature private messaging, job management, invoicing and a way for both the seller and the buyer to mark jobs as “complete” and be paid for the work.
- This is an ironic one – but I intend to build a theme! This theme will be lightweight and built as a child theme to Themedd (the official EDD theme). It will support lots of useful features to help you create a digital download or service-based marketplace. This will also integrate nicely with my new audio player!