Eight days may not seem quick but that is the length of time ebay give a buyer to pay and you have to live with that. In fact if they paid by echeque in the last minutes of day 4 it would probably take longer than 8 days.

If you don't want to wait for buyers to pay, and I don't really care how long that is as long as I get paid or they get a strike, you should list all your items as BINs with instant payment required.