Ebay in reverse

I can't really claim this is an original idea. I definitely thought of it on my own, but in searching to see if it already existed I discovered that someone else had the same idea I had.

That idea being that ebay really ought to be able to work in reverse. As in I tell it what I want and am willing to pay and then sellers can come and find me. This would also work really well for services, not just goods.

I double dog dare you to tell me why this wouldn't work.