Another giveaway that you're playing a sandbagger is when they make rude comments during the game, something like - is your rating really that high?
An experienced player can usually tell quite quickly that someone is faking their low rating, or else that player is cheating.
I once spent an evening showing a beginner friend of mine some of the classical games from the past. Games of Anderson, Morphy, etc. He was amazed by the beauty of these games.
He asked "Can you play like that??" He then challenged me to get on Chess.com, challenge players <1000, (much lower than I usually play,) give away my queen in the opening "Scott free," and try to still win.
I played about a dozen games. I couldn't get anybody to take my bloody queen. No matter how hard I tried to sac it. Or how obvious I made it it was hanging.
Then I started thinking "These folks may be trying to lose on purpose...."
I could understand maybe one of them trying to lose on purpose, but a Dozen or so ?? uh-uh, I think they were just some really sad sac players, possibly just branching out from checkers for the first time ?