Well, you can charge for the software as a whole, which I read your comment to claim you can't. I can absolutely say, hey, here's AwesomeDebianFork 1.0 with some custom patches on GPL code, you can get a CD set of binaries + source for $99. I don't have to resort to circumlocutions about service, and I don't have to make the source available to anyone else. (
You are free to copy that source CD, though.)
The only thing I can't do is to say, the CD for AwesomeDebianFork 1.0 binaries is $9 and the CD for AwesomeDebianFork 1.0 sources is $90. (The GPL would reject this as not being "reasonable"; the DFSG would reject this outright for violating #2, "The program must include source code".)