While some sellers will wait longer than others, the seller can open an Unpaid Item Dispute 96 hours (four days) after purchase.
Then it takes another four days for the dispute to close if the customer does not respond/pay.
The seller gets her fees back. The buyer gets an Unpaid Item Strike.
Sellers can Block automatically bidders with UID Strikes through their Seller Preferences. There are a few other useful Blocks there.
