I honestly have never been to an auction house (or simply can't remember going to one) but I imagine that many things get sold for a good price. Even with eBay, there's no guarantee of a sale as you're competing with so many of other sellers.

Having said that, if you know how to offer something that people will buy, then yes the 7.9% fee is nothing. If you think the fee is too high, either adjust your prices/selling practices or don't do business with eBay. A big company like eBay won't change their fee rate much, as they already offer lots of other incentives.