Yes, I have, and I was upset doing so. I joined a league to play and compete, not to show up, spend time and money and lay down. I was a SL2, and could not afford to move up on our team because of other players numbers. Fact is, I couldn't move up even if I tried. I knew very little about the game.
I've been to many money tournaments and city qualifiers, and this is where sand baggers breed. People play as other shooters, they shoot a limited number of games during the regular season, whatever, and show up and blast the competition. I've heard at some national tournaments, you would have to throw the whole room out to get rid of all of the cheaters who show up.