Then you're either out in public, and they can retroactively fix the bug, or you're trying to sell them privately, in which case you're not gonna have much impact anyway.

It's the same as with hacking in mmo games. No one cares until you start publicizing your hacks, in which case they can just install your hack, see what bug it's abusing, and fix that.

Seems like a very small market to me: people willing to spend money on the game, but not spend that much money. Most cheaters want to spend $0.