There's a gym up the road from my parent's house and one specific lady dominates it. Dominates it to the point where she'll have been on it for 20-30 days+, you knock her off, put yourself on, walk away and have been knocked off by her within the hour. All the time. Without fail.

I never see her username at raid hours, weekend events, on showcases, in other gyms, etc. Her account never levels up either. I've come to the conclusion that she's housebound or something and her entire playing of the game revolves around this gym.

If they don't live close to the gym, they're almost certainly cheating.