Anonymous source? Is it that he can't trace the transaction through the alert or he doesn't have much information about it. No matter what, don't use your credit card on unrecognize websites, use other options to deposit. Now that we are in the era of crypto, there are vast options gamblers can use to fund there casino flawlessly and less complicated because you don't have any fear of this kind of things, you just deposit and that's all since international transaction are complicated and slow.
Credit cards are actually much safer to use than cryptos. They have a user protection in which you can get refunded and then the scam transaction will get blocked. When it comes to ease of access, it was also actually the credit card is the one that is easy to use because we can just scan or swipe them.
To OP, a gambler is only a scam when casino do some obvious manipulation, cheat you, clear your beating logs and refund your balance
Gambler? Maybe gambling sites you mean? Some gambling sites can do a manipulation but I think this is still far from a true scam since they can still make some payments. And I don't think a casino will clear our beating/losses logs. Logs are always there and it was only losses anyway. What benefit can they get from doing that? A scam casino won't also make a refund but even the legit ones can rarely or won't do it at all. It is our full responsibility when we play gambling though.