A sales enhancement for both stores and auction would be the ability to offer quantity discounts. Buy 1 of a certain good, you pay the posted price, buy 5 you could offer say a percentage or a flat dollar amount off. Buy 1 piece, you pay the posted price, buy 5 pieces and get 10% off or $5.00 off, etc. It has been well demonstrated that quantity discounts are attractive to customers who need to buy more than one of something.