Here's the thing: some people have learned to do TK. In one Air Force report, it was noted how AF generals often got together to see who could bend the most spoons and forks. But in the real world, being telekinetic doesn't enable you to move cars or any of the spectacular crap seen in movies. Most teeks can barely move a quarter or push a soda can. Russian telekineticist, Nina Kulagina could telekinetically lift a 1 bs book at most and there hasn't been anyone much stronger than her-- at least that anyone knows about-- but there are a lot more weaker people than her.
But if one did have enough control, it wouldn't take a whole lot of power to affect a roulette wheel in a casino. However, casino people aren't stupid: if someone started winning too much it's a good chance that that person won't be allowed back, or might come back with broken knee caps. despite what some people think, both casinos and lotteries know that maybe 5% are psis and as long as that they don't win too often, there's no problems. In fact, one person winning a bit more is a good thing as it inspires others to gamble and to loose. But when a psi gets greedy and starts winning too often, they can be cutoff rather rudely by the casinos and lotteries.
It's also a bad idea to jump up and tell people they are psychic and can win a lot telekinetically or through precogs abilities. When you attract too much attention, friends will drive you crazy asking for you to win for them and strangers will be even nastier if they thought someone could make a fortune just using psi abilities. A teek could make a lot of money, but they would have to be extremely careful in doing it.