If they are challenging you to less than 5 minute games, they can't really cheat, unless they're using a bot. They'd probably only challenge 2200+ in those cases to fain the most points.
Lol, not how points work.....above a certain level it would just be +16 (assuming they have normal RD). I have noticed that the rating gain corresponds to the win probability and so +800 is about 1% chance of winning, and so i mean 800+ and you get 99% of your k-factor, so playing OP or playing a 2200 wouldn't be meaningfully different. To be fair, not everyone may know that.
If they are challenging you to less than 5 minute games, they can't really cheat, unless they're using a bot. They'd probably only challenge 2200+ in those cases to fain the most points.