Which pokerrooms can be trusted?
Obviuosly not all pokerrooms can be trusted, I recieve lots of spam mail from sites advertizing huge bonuses and I would never consider for a second to use any of those; either they are scams or even simpler, from sheer principle: You should never reward any spammers by accepting any of their offers.
How do pokerrooms make money
You should be very aware that pokerrooms make a lot of money whether you win or loose! When you win, you win other players money and when you loose, you loose your own money - but no matter what the pokerroom will get their “rake” which is a small percentage they take from each pot. The rake is normally around 5% on cash games and a little more on tournaments, around 10% to 25%. There are many different ways for calculating rake, but this is the primary way that pokerrooms make money. Since they profit whether you loose or win, they have no reason for trying to cheat you and should they do anyway, they put their entire business at stake. So I don't worry too much about whether I will get my winnings or whether they will empty my credit card or bank account. It should also be added that in Denmark where I live, we have laws to provide a high degree of protection when using online transactions in general.
Other ways to get cheated
When it comes to real cheating there has been found examples in the past, and lately there was an example of cheat at absolutepoker.com where a cracked version of their software permitted a player to see his opponents cards but this is very uncommon.