>So, one more reason not to trust people who sell protection.

Yep!!!

>What I believe that happens here is the following: they simply "brand" (that's the word they use) your source code with a special mark, which their own de-compiler recognizes and respects. Your source code, or compiled code, isn't really encrypted or something, when you brand it.

That's close to what is happening...it also makes some changes to the vfp runtime files.