If in doubt ask yourself this question;

Is it too good to be true?

When there is doubt in my mind about something then I ask this question.

As an example, we recently saw some offers of 1 year Yahoo listings for $50.  The usual price is $299.  Dozens of people paid their $50 and were listed on Yahoo within about a week.  It was great.  The others kept coming and people’s sites were listed on Yahoo.

How you ask?

Well, the scam artists were using stolen credit cards.  Eventually the credit card charge was reversed and the Yahoo listing  was removed.

If it is too good to be true then it probably is!

edited: June 2009
Here are some examples of this scam in action.

http://forums.digitalpoint.com/showthread.php?t=999507

http://forums.digitalpoint.com/showthread.php?t=844628

http://forums.digitalpoint.com/showthread.php?t=887950

http://forums.digitalpoint.com/showthread.php?t=876472