IMO, cheating is a big problem with on line sites.
If you talk to on line poker room managers they can tell you some horror stories.
That said:
When I started in poker about 1960 in KY, cheating was rampant in poker games. Same as on line sites except they used divices such as shaded cards, shaved cards, etc.
An old timer told me, Learn every thing you can about all the ways to cheat, watch the game, figure out who is doing what, and say "deal me in."
That advice has worked for me since the day it was given.