actually thats not completly true there are independent groups that can investigate and verify if a poker site is legit i think there have only been two to do so i think one is
poker stars but if a poker room was to be "rigged" then people would know because lets say a certain draw is known to catch 33% and that is a cold hard fact and someone has 10,000 hands of data and its not even close to that percentage i.e. +-5% then the site could be messed up. I suggest if you really dont trust a site then get something like pokertracker get a lot of data and check it out for yourself.