If they're so worried about us cheaters getting achievements, they should just follow Fallout's way and disable achievements when cheating.
If that's to hard for them to code, then maybe they should practice the phrase "you want fries with that" and get a job selling burgers.
if you use the built in cheats they do disable the achievements, the trainers circumvents this so you still get achievements.
so if you want to cheat in single player your best bet is the type in codes built into the game.