I usually state in my auction that newbies should send me a quick note to let me know they're serious about bidding.
Although I've had a bunch of 0-5 feedback people promptly pay for their item, there have been an equal number of Nigerian scammer types, who send me faked Paypal "You've got money" emails, or ask to pay me via Western Union.
Generally, if there's a 0-5 feedback bidder who seems to be actively entering in bids, I send them a quick note, asking them to reply. None of them ever do, so I cancel their bids.