A few questions and why's

Why don't posters post the price a lot do but the ones that don't can waste the posters time as well as the buyers time if the price isn't posted.
Can't that be mandatory to post??
also any thoughts on being able to have a feed back so the buyer as well as the seller knows who ther dealing with????

Don't know if this was coverd before but thought I would bring it up again if it was
Thanks
Larry