Exactly, bets would be a scam if your funds are frozen without reason, if you win and your bet disappears, if the game is rigged, or if it pays less than it should—it could be considered a scam.
This can be easily control by using a trusted gambling site. I can say this isn't common. And if it happens, the gambler most have been tricked to their gambling site with their fake promotions.
There are many trusted sites that advertise their platforms on this forum. Gamblers can choose one of them to prevent falling into the trap of fraudsters who exploit online gambling platforms such as bonus abuse, affiliate fraud, unfair practices, money laundering and user data security.
Yes, there are many gamblers who still become victims due to choosing the wrong platform, this is also not common because it is done by some people who are only looking for personal gain by harming others.