Try calling an airline after you've ordered a ticket online to explain you can't afford it and want a refund. Just because it's ebay doesn't mean it's any different.
When the order is binding, has much to do with how the ToS of the site/store is written. Some sites take the attitude that an order is not binding (on the buyer or seller) until payment is made. Some sites take the opposite view.
In some cases it gets rather squirrelly when you have a seller with a limited quantity of the item (like 1 or 2) and a buyer who wants to use a very slow payment method (check, MO, etc). What do you do if the buyer wants the last one, in a hot market, but also wants you to wait week +/- for payment ?
Beyond that grace period they'll usually charge a fee of some sort, and the refund might be in the form of a voucher or credit.
If they do, they would use the court system, they wouldn't use a well known con to recoup their loss.