It seems to me that all this change of rules is doing is just simply shifting the administrative burden away from staff, to the seller (and lesser degree, the buyer). This seems pretty damn fair to me, since they are the parties who are profiting. I like the way people are offering to edit in relevant questions PMed, that is very classy.
I think the only real "loss" I see is the ability for a random user to dutifully whistleblow if they see some falsehood/scam. Luckily it doesn't seem to be an issue around here, but any solution I could think of involved staff headaches, so it is kind of a blind spot.
I also suggest noting the date of any price drop in the thread title to attract attention.
I agree there should be a rule regarding locking/re-listing to jockey for top position.