This fun venue for buying/selling gear would be GREATLY improved if sellers left prices up. The main reason is it helps Everyone "appraise" the value of any given item, by seeing what the "market bears". Look at the last 3 that have sold, average the prices [holding certain variables constant] and you have a general idea.
Without this, sellers often list used gear at 90+% of new retail, which makes me laugh, and buyers lack the ability to appraise. This is where we can learn from eBay's success. There you have a much greater ability to establish fair market value based on appraising sold items, and the transparency benefits all.
At minimum I suggest: sellers leave their last price up, and if it matters to them, they can indicate 'SLAP' - Sold Lower than Asking Price.
In the end, the transparency would improve our venue overall, as sellers will always highball, and buyers will always lowball, but what things "are selling for" will always define reality.