There's a few ways we take care of this:
Automatic scanning of trophy hacks
If detected, this results in complete removal of your profile. This cannot be undone unless you can show a certain game can be completed in a way that looks hacked.
Automatic scanning and flagging
A similar system is in place to automatically flag games but this only results in leaderboard and achiever list removal. You can hide these games to be reinstated and they do not count towards the leniency limit.
Someone reported you
These reports are checked by staff. If valid, the game is flagged and you are removed from leaderboards and achiever lists. You can hide a maximum of 2 flagged games and still be reinstated. If you are flagged in a 3rd game you cannot be reinstated.
What you see
If you're flagged and can hide some games
If you're over the limit