I just read about this simple but scarily effective hotel scam that I could see myself falling for. From Hotel Chatter:
'This is the front desk. When checking in, we came cross a problem with your charge card information. Please re-read me your credit card number and verify the last 3 digits numbers at the reverse side of your charge card.'
Not thinking anything you might give this person your information, since the call seems to come from the front desk. But actually, it is a scam of someone calling from outside the hotel/front desk.
So if you do get a call like this, go down to the front desk and check it out yourself (or at least hang up, then call the front desk so you know who you're talking with).