You are in hotel and just settle down in your room, after a long trip. The phone rings. "Hi, this is Mary from reception downstairs, sorry to bother you. We're having trouble with your credit card--the numbers can't be properly processed. Would you mind double checking it with me, so we can do it manually?" "Sure. Do you want me to come downstairs?", you say. "I wouldn't want to disturb you more than I already have. Just read me the numbers and I'll make sure they're accurate."
Unfortunately, "Mary" is not working for the hotel; she is working for your money, and she's done a pretty darn good job of getting all she needs. Scammers usually call room numbers non-stop, until they find somebody who just settle in and really believe the card transaction didn’t go through.
How to avoid: simply head down to reception if you get a call like this. That way you can be sure who you're talking to.