Dymond said:
"Yes" is the answer to both questions.
Yes some people win and make a decent ROI on it (depending on your definition of "decent ROI", obviously).
And yes, it's very hard to do consistently. In addition to finding ways to consistently pick winners at a rate that beats the vig, you also have to play the metagame of not getting banned or limited by your sportsbooks for being too successful.
Once I wanted to try my luck at soccer betting so I deposited 10 dollars or so. Since it was my first time ever playing sports, I tried betting on some certain wins even though the winnings would be like 2 cents or something. Milan would be playing against a third category team. Nope, still lost.
I can tell you first hand you can make a living off of this but you must also be wise always good to have funds saved for any and I do mean any set backs be smart but try to have fun don't let the money take away from the passion you have for the game it self then that can make it complicated good luck to you
