Most of the casino works with big money, So they won’t scam for the little money. Which you mean as the bonus to the participants, the bonus is nothing to the trusted gambling or casino. If you want to check to find the bonus program of certain website, you should apply for it. Then check whether they paying you the bonus or not. The good gambling site ready to pay you even 1000 dollars as a bonus for the big deposit. Bonus program is used by the website to get attractions among gamblers, I don’t think they will scam on such program.
Some casinos work by cheating small money so it's still money for the casino. They will not hesitate to take it from gamblers by beating them in gambling games. We often hear that many people have experienced defeat at gambling and even though they took promotions and got bonuses, many gamblers have lost. So if the casino is a scam, the casino will use all means to take the customer's money and even if the customer complains about the problem to the support service, it will not be resolved properly.