I do believe that you can “Mark” the non-payer on the page where your work is managed (Edit, mark as sold, etc.) This stops them from bidding again until they pay you. Also, have you tried contacting Dave? I believe when you first receive the email notification that your painting has sold, on it is a way to let Dave know of the non-payment.
About the $ 30. sale price…that is why I really don’t have anymore auctions. I’m limiting what work of mine is on etsy in hopes of working with my collector email list and my own website. - Brande