That is the problem that I have. Someone, usually a noob, will find an old post and respond to it, bumping it to the top of the list. Then, as I see the post, I get excited about a "new" item for sale. (Yes, I have premanent GAS!) If the when-posted date was in the initial window/item listing, then you would know right off if the post was 2 or 3 years old or if it was new.
Maybe it is just me ...

I am just trying to save time from having to look at every post each time one jumps to the top ...
