In short, an auction is a game of chance—you may have some items for which you get good prices, but most of the time prices are at bargain levels. Often, pieces are grouped and sold a as a lot, and some lots go for very little value. Many auction houses charge a set-up fee, as well as a tear-down fee. There is often a charge for advertising.
In an estate sale, every item is priced individually individually. By doing this, we obtain maximum value for each item. We also have specialty buyers, and internet buyers, who pay higher fixed prices on special items.