[@sambauers Participant 16 years, 4 months ago]

If someone takes your GPL work then modifies and sells it, that is not against the terms of the GPL provided they distribute it under the same GPL licence. That means that anyone who has the modified source code (and every purchaser should have it) can redistribute it for free again (under the GPL license).

If they are distributing the themes under a different license, then they are breaking the terms of the GPL.

If they are compiling or obfuscating any part of the program and not making the source code available to those they have distributed it to, then they are breaking the GPL.