Actually, Neil, there was an account @cjxchess16, his account got closed due to multiple games in which he sandbagged.
Also, reporting can work, they will get a warning, I think, but their account might get closed, or muted. Depending on the situation. Sandbagging is quite a serious matter.
What's hard to prove about a bunch of 0 move losses?
If it is that blatant it probably wouldn't be that hard. However, I still don't think chess.com would care as much as they would for engine use since what upsets people the most is when they lose to people they think are cheating. That is what chess.com would make it their priority to eliminate. Every once in awhile I will play a move and then someone plays a move and resigns, but I just assume they had to leave since I also do that when something comes up. I just start a new seek so I can keep playing. They could have been sandbagging but I wouldn't know unless I looked them up and checked their game history.
I was once playing crazyhouse against someone who was higher rated but kept playing ridiculous moves and losing. He told me after a few games he wanted to lower his rating so he could surprise people in an upcoming crazyhouse tournament. I stopped playing him since the games were pointless but I didn't bother to report him and I think people like that would probably never get banned even if they were reported. There is no way to really prove it by looking at the games.