Trying it is still the best way for you to confirm if something is a scam or not, but you don't need to deposit your bitcoin on some fishy site, I mean you could use the free satoshis that they are giving in their faucet, then, if you can't withdraw your winnings, then, it just mean one thing, that they are not legit and you could accuse them as a scam, because sometimes, other people are just trolling other people.
You really cannot determine whether the site is a scam or not when you are trying to withdraw small amount of coins,since the price of bitcoin is increasing you should expect more ways from scammers to skim away your coins but that does not mean that every new gambling site that appears are going to run away with your coins but it will take some time to get the required trust from the general public and if they are transparent then there wont be any issue.