I my experience selling the bad ones are a very very small percentage. I don't think I have ever had a non-paying bidder in the past couple of years I have been selling items (bike related or not). While some of them are not the quickest to pay they have all eventually paid. The longest I waited for payment has been 5-6 days after the auction was completed and I sent and invoice with a total amount. In my experience the international bidders are usually one of the first payments I receive or the first to ask for a total.

If you are selling valuable vintage bike parts open it to worldwide bidders. It is more of a pain with the customs form. If you get paid with paypal, paypal takes care of all of the filling out the customs form so it isn't that tough. Plus, I have found I get much more on many items with bidders from different countries trying to win.