Can I suggest some compromises?
I HATE the bumping constantly, it makes it impossible to find stuff that has been listed recently and is probably still available. It was like walking through a market place where you can only buy from the loudest sellers.
As I have said before it reminds me of the seagulls on "Finding Nemo", but instead of "Mine, mine, mine, mine, mine!" I hear "Buy, buy, buy, buy, buy!". I have even been onto threads and said "please can you list what is still avilable from your list of 546 nappies", only to be ignored.
Have a for sale chat if that is what you really want. Have it in the for sale section when they bring in categories. Have it as a category. I really dislike this idea, but if MN needs the page hits for their revenue (something that I doubt many of the "cheaper than ebay" people care about) and that is the the only way to get it then have for sale chat.
But keep the for sale threads as they are now, listed by time posted, and easily brousable by the "not a regular for saler are you?". It is for sale and you should be listing what you have for sale, not chatting about how mummy987765433 is a scammer and never delivered your farkaboo lillywank in snot green.
It would be much nicer if you came and joined the rest of MN (those of you that don't already). It would be so much nicer if you went and helped the people who are posting about needing help (as I am about to do). They realy don't bite, really