I played on the weekend in a group with a guy i'd never met who had a handicap of 10. I wasn't scoring his card, but my mates instead who I play regularly with. We always play by the rules, as we are both trying to improve and believe this is the way to know correctly where we are at. We usually score in the high 90s, low 100s.
This other guy had two drops, two blow out holes, no birdies, and a couple of bogeys and double bogeys. He wasn't happy with his form on the day either. At the end of the round we had a look at his card and his marker had him down for an 83 off the stick, 12 over par, which was impossible considering what we'd seen. I was really taken aback that someone with a low handicap like his would cheat at least 5 or 6 shots.
I believe a lot of people fudge their numbers every round, not just high handicappers using shoe wedges and gimmes etc but low handicappers as well who are desperate to maintain their bragging rights with their mates..