Forcing a seller to list a price matters to me. I like the old fashioned school of bargaining, its fun.
If a potential buyer doesn't want it ... pass on by, who cares, I don't think you're hurting anyone's feelings.
Generally back in the day, book sellers used to have integrity, really !! However now, book business is about 98% bullshit, deception and outright lies.... Including many of our very own DT.orger's, (y'all know who you are) But unfortunately there's no way to fix that.
Ebay (in the beginning) was fun, now it sucks, I avoid buying there when possible. Same with Paypal, it sucks, but not much choice if you want to buy or sell on eBay.
One of the many reasons I joined DT.org was for change from the norm (eBay & such), another avenue, it's a nice place to visit. And... I found an amazing family of obsessive compulsive geeks just like me.
Adding more rules because somebody else whines about the current norm makes zeroooo sense.
I seem to remember one of the biggest complaints about another similar site was rules and policeing.
... just a few thoughts.