Sandbagging is a violation of the terms of service and is considered a form of cheating. You can certainly report it. Others have noticed as well, judging by all the previous threads on this. Thought you might want to read a few, so...
https://www.chess.com/forum/search?keyword=sandbagging
I've bumped into this a lot. I don't know how many else is really noting that some players throw up games. And the clear reason behind that behaviour is to contest in the lowest-level tournaments (max 1199).
I started noting when contesting many tournaments and thinking - that player won the tournament and raised the rating over - now (s)he has lost games and came back. Yes, that was the case. But then I started to look at games between tournaments and it was really fishy. Either resigning several times after one or two moves or missing the threat on queen something like five games in a row.
I think this harms many players who contest the tournaments, me included.