Send it to spoof@ ebay.com.
They will tell you if it is fake.
If the seller has opened an Unpaid Item Dispute, it will be on your eBay Messages page.
You can look on your purchases page and see the items you have bought and their payment status.
You can also check your PP account and see the payment.
It is just barely possible that you sent the payment to a dead account. Unlikely.
It is also barely possible that the seller sent you an invoice that crossed your payment in the mail.
And obviously, don't send any money until you are sure of the problem.
If your paid item does not arrive in 20 days from payment (15 fromEurope, 30 from Asia), go to the bottom of this page and open an Item Not Received Dispute.
You have 60 days to leave feedback. Get this cleared up before you do.