Go to your Seller Preferences and set your Blocks against bidders with Unpaid Item Strikes.
You can also Block bidders who do not have active Paypal accounts, but if you get a lot of newbie buyers, you may lose them too, since many newbies don't think about how they are going to pay when they bid.
If you use Fixed Price listings, you can further make your items Immediate Payment Required, but this doesn't work on auctions.
Meanwhile, worry less about feedback and more about your Detailed Seller Ratings. For whatever reason, three of your DSRs are showing as 4.5, perilously close to 4.3. At 4.3, eBay starts restricting your ability to list and sell.
Preventing feedback also prevents DSRs being trashed. If an unhappy (or nasty) bidder could leave feedback, it would be worse for the seller than leaving negative feedback would be for the buyer. Keep in mind that most sellers do not use Auctions and do not have the opportunity to vet bidders before they buy.