How about a visible voting system (or something like that)?
Basically; when members see a for sale thread they can upvote it (regardless of whether or not they themselves intend to buy it), and the # or % of upvotes would corelate with a hot/cold or 'popularity' metric, which, ideally, would be a visible...thing? e.g lots of upvotes = a 'red hot' indicator = more leniency with bumps (because the community believes it will sell and is ok with seeing it bumped), and 0 - a few upvotes = a 'cold blue' indicator = less leniency with bumps or automatic archival of the thread (because the community doesn't believe it will sell and no longer wants to see it being bumped).
I hope that makes sense...
Basically; when members see a for sale thread they can upvote it (regardless of whether or not they themselves intend to buy it), and the # or % of upvotes would corelate with a hot/cold or 'popularity' metric, which, ideally, would be a visible...thing? e.g lots of upvotes = a 'red hot' indicator = more leniency with bumps (because the community believes it will sell and is ok with seeing it bumped), and 0 - a few upvotes = a 'cold blue' indicator = less leniency with bumps or automatic archival of the thread (because the community doesn't believe it will sell and no longer wants to see it being bumped).
I hope that makes sense...