One of the things you'll see on a genuine ebay email is their cautionary notice to NOT give out your credit card info nor your password nor any other detail that would compromise your account. If they really have a problem with your credit card or something, they'll find a way to notify you... such as a 'bounce' or rejection of your card when making a purchase.
For those that have MBNA credit cards, have you ever used their ShopSafe option? It is a way to create a unique 1-time only credit card number that is mapped back to your existing card and safeguards you from someone picking up your card number from a transaction and loading up charges before you can detect it. I highly recommend it. You can find a demo at
http://www.mbnashopsafe.com/ and see if the offer would help. I'm not sure it would help for accounts such as paypall where your card info is retained for future transactions.
