Auctions totally make sense if you really don't know what something is worth. Start it at the least that you would reasonably be satisfied with, and see where it goes.
If you know what something is worth, sell it at that price. Start high and drop if you need to.
Of course, I always think as a seller, even when I am buying. I just look for sellers' mistakes that might be to my advantage.
I can't imagine paying half the price of an AT for an XT, but it looks like people will do it.