I'm not sure of the answer either - but I know what isn't the answer - I recently purchased a premium plugin for a client to use on one of his sites - the plugin is well made, does exactly what it promises, and does it pretty well. It's a membership management plugin, and as part of a bigger site, it needed to be pretty closely integrated with a few other components.

I was happy to pay for the plugin, as it goes above and beyond your average plugin fare - I was even happy that I had to enter an activation key to register it for the site - a bit more hassle than I expected, but I understand that the developers feel like they need to protect their assets.

I got to work putting the site together, and I got to the point where I'd need to do a little custom work to integrate the membership protection provided by the plugin with a forum, to protect that as well. Assuming the code would be as pretty as the interface, I didn't have any worries. Then I got into the plugin files - and the ENTIRE THING was encrypted. (I'm not sure encrypted is the right word here - obfuscated? I've never needed to do that before, so I dont know how it works) Every file. Every last line of code.

I'm still furious about it. I was on a deadline, so I had to use it anyway, and just guess at what was going on in the database - thank goodness they didn't find a way to encrypt that. $100 for a plugin that I couldn't extend at all beyond the out of the box functionality.

I'm happy to pay for plugins - and honestly, I'd like to sell a few as well - but please, don't render your plugin completely useless to another developer like this.