It can be very difficult to spot a scam. They're getting very good at making their outreaches look legit. So how can you tell whether or not something is a scam?
Easy.
In every case, they contact you first!
If you recieve some sort of contact about your card, ebay account, paypal account, bank account, etc. and it sounds like it requires your attention - don't click on the link, don't talk to them on the phone (hang up!), don't engage any written or verbal dialog in any way whatsoever.
Instead, initiate contact with your credit card company, bank, ebay, whatever through a legitimate, known means that you know for certain is legit.
Example:
Credit card company calls you to investigate possible fraudulent charges on your card. They want to know if you actually made a few recent purchases.
HANG UP!!
Now, look at the phone number listed on the back of your card. Call it, and ask for the fraud department. Then ask if they're trying to contact you about possible fraudulent charges. The conversation will flow from there.
In this case, you know, beyond a doubt, you're talking to the real McCoy and not a scam artist.
Make sense?