Such casinos usually use gamblers as a tempting bonus, if a gambler deposits there and the gambler directly they will not be able to use that deposit bonus. This is true because it is better not to enter such gambling sites, and if you accidentally create an account on such a gambling site and deposit, you will be hit repeatedly and you will have to lose your money intentionally.
And if the money you deposit and gamble or win at the casino is more than the original balance, you will have trouble withdrawing it and will repeatedly throw you into confusion. So it is best for everyone to be careful of such gambling sites, and it is better to use trusted gambling sites.
That depend on the casino because if that casino is trust and have reputation, they will give the bonus to their members because that is one of many ways that they can do to make their members stay in their casino. But if that is a scam casino, people must be careful and not deposit on that casino or stay away from the casino. We don't have to risks our money in a wrong casino so that is why we must research before we decide. We must know how much money we use to gamble so we don't have to spend too much money in gambling. That is what we must do to prevent the big lose in gambling while we only need to enjoy the gambling as an entertainment.