Sports betting is really risky most of the sites you have mentioned have limitations in the amount of money you can win and if you want to withdraw your funds they ask for various verification and finally you don't get anything stick to
Not that "really" risky. It will be "really" risky if you'll bet to the teams that you don't have an idea on how they play and you don't do analysis for each fight. Sports betting is like playing poker, you need to observe the odds, make sure that you can take the risk and if you can't just fold(don't bet at all) if you are not sure of the teams that you'll bet, this how should someone start with sports bet.
i agree with bhadz said because we only spend our money without any clue or anything about the team. its better to place a bets for a sports that we know like football and if we know one team or more, then we can have a chance to win. but before you involve too deep in any of gambling games, my suggestion is don't play too often because you can be an addicting person in gambling.
You can also try out some casino's that are offering play money if you are not sure of it. And well your experience will be your mentor once you are starting to gamble with sports bet. Things will just be learned base on what you are doing and suddenly you'll become a risk taker when you want to try some more. I went through to that feeling when I was still new and wants to learn more about sports betting.