Thanks Stewart for this post.
I'm totally agree with you here.
If Mr. X want to sell his object I thinks he shouldwrite the price he would like to receive.
Maybe the best offer near the price requested...

I also don't like the auctions on the forums as nobody can see the other offers and have to trust on the seller words.

Different is when, in privat, Mr. X ask to Mr. Y one of his watches that are not for sale. In that case I find correct a Mr. Y question:
"Thanks Mr. X, the watch is not for sale but if you want to send me an offer I will take it in consideration and let you know".

My thoughts
Best
Giuliano