For my sins, I've seen the last few United games and the West Ham one aside, it's not as if they've not had decisions go against them either. There is a bit of selective viewing here, with some of our own challenges too.
The standard of refereeing over the last few days has been shocking but I still believe that is down to incompetence and potentially a small amount of unconscious bias rather than anything overtly corrupt.
I read an article a few years ago about the Italian match fixing scandal and the main way that refs influence the game is by decisions on 50/50s in the middle of the pitch and use of the advantage rule, and it is around ensuring overall control is kept by one team. It wasn't ever something as blatant as a dodgy red card or penalty that was outside the realms of interpretation as that would be too scrutinised post the event.
There's been a few games where I thought that could be a possibility. I tend to err more on the side of incompetence though and the difficulty of interpretation nowadays, particularly with red card offences.