In my opinion, if someone wants to cheat in single-player, more power to them. I don't really care. Cheats can be fun.
But if you're worried about save/load codes or the like, you have a couple options:
1. Make the code different for a single-player game vs. a multi-player game.
2. Don't let people play in single-player mode.
Also, Cheating Isn't Chatting.