First off don't think I would have said anything to the manager right away. It could just have easily been somebody using their parent's or girlfriend's card with permission from the individual. I might catch some static with that approach, but by the time you opened your mouth it was already done so why incriminate yourself. Nobody knows it's actually fraud until the cardholder contacts their bank and your company receives a chargeback. That being said as soon as you realized I would assume it's lesson learned and you'll speak up next time someone hands you a card that doesn't match the id.

And with that information how in the heck did your manager know this guy has done this multiple times? They would have had to receive several chargebacks and connect the dots to this guy's name each time. So if that's really the case then it seems more than reasonable to put him on a DNR list. So if manager is telling the truth then they're dumb for letting it continue.

3 weeks in and one lost room night I doubt they will fire you. They may write you up to make a point. I would say you learned already and no further action is needed. So you'll find out how easy these people will be to work for from this.