choosing the right online gambling casino? That may be a bit difficult due to how much research you should do before trusting them (or anyone running centralized services) with your funds. Bitcointalk is a very active and morally conscious place and we have a very active sub-forum for gambling. So everybody is always looking out for bad and good casinos. A lot of data can be found in this sub-forum. Other than researching, I guess I would have to say you need to try a few casinos out for yourself if you want to understand when you find a "good one". Its all a subjective experience.
But unfortunately, many people don't do their own research and just rely on other people's opinions so they can get into trouble later. I agree with trying several casinos and comparing them so they can find the casino they want. This will keep them out of trouble because they really only choose the casino they want and of course, that casino must have a good reputation. By trying one by one, they will get an experience for themselves that can be shared with their friends. And they also have to remind their friends always to research each of their casinos.