Take a look what other people say about it, where they hangout and what kind experience they have, that is the best way to know is some gambling site scam or not. If many people play on some site and they have positive experience then it will he good for you too. Casino will not risk good reputation to scam one little player, you can relax and follow others who probably risk more money then you do. This forum is the best place for that, you can check out many casino's, you can see who plays there and their experience, and maybe the best thing is that you can talk with each of us, send some PM and we will respond, something like 24/7 friend support.
I'd say that there is no other way to check whether a gambling site is a scam or not, you can just follow what is said in the quoted post above. Only I would exclude sending PMs. The thing is that reputable members of the forum are too busy to respond to every PM sent by strangers, and, in addition, you can be misinformed communicating via PM more easily than when you do it openly on the forum. That's what the forum is for, you can see the reaction of others on what someone is suggesting you.