How to block zero feedback buyers

[smokinjoesp1]

I sell computer hard drives that are quite expensive and I keep getting scammed by zero feedback buyers.  They buy a drive, I ship it and then once they receive it they claim it was an unauthorized purchase.  Yes PAYPAL covers it, but I have to send them proof of delivery and then often follow up to make sure they remove the reversal.  One way to stop it is to figure out how to block buyers with zero feedback.  is this possible?  I tried to do it on my setting page but it didn't stop this latest scammer.