Normally a fraudulent seller wouldn't put a buy-
it-now price on an auction, they'd want people to 
bid it up as high as possible. 

To be safe, you could also send an email to the 
other ebay user that this person said they used 
to use, just asking for confirmation. And if you 
mail the payment, send it with delivery 
confirmation. An honest seller should understand 
that a smart buyer takes steps to protect 
himself/herself. It doesn't mean you don't trust 
them, it's just being careful.

Good luck,
Skorp