Even though I have done this one time a while back,
Threads that do not have prices are very stupid. It allows the seller to not only feel the price, but also call when it ends. It's sort of a way to gut people for th most money possible. Not going to lie, this was my exact thought process when I did make one thread, but its easier for everyone if there is a set price that can be manipulated downwards by the seller, if there is not interest.
Long story short, it's an eBay auction that never ends, allowing the seller to get the most moolah.