Some people are just really inconsistent, I happen to be one of the players in that category. I get accused of cheating fairly often when I beat higher-rated player on FICS, but it's really just that I'm having a good day. In fact, that's one of the reasons I play as often as I do; it's a good reality check for how well the gray matter is functioning on that particular day.
Good point. Only i'd say that sometimes i have not good but bad days and my rating is falling down much. Couple weeks ago i was under 1200 and now i'm around 1500. Was i faking? Of course not. My brain wasn't functioning 100% those days. Probably some people are rated 1100 thought that i'm a sandbagger. I'm just not stable.
Most player's hover around a different rating than the outside world. My club rating is around 2035, but here I'm currently at 1800, but with all these chess engines, and other stuff I probably will stay around 1800-1900s doing online chess.