Most coins, already have a set value. What would the be the point of an auction site? Why would anyone want to pay more, or anyone want to get less, then you would if you buy/sell on an exchange?
perhaps for new coins before they hit an exchange
Basically for that reason in case an exchange isn't offering yet or someone doesn't want to go through the hassle of an exchange or even know how about going to make a trade. A simple ebay style setup. Really though it would be better for the sellers at this point for an auction site as have you seen the prices people are paying for them on ebay?