Probably the fact that someone with 31 posts in 8 months and one purchase transaction would have such a great idea as to what it would take for this forum to operate properly.
Like stated earlier, just replace the price with "SOLD" and don't do stupid post-sales bumps. The threads will die naturally that way.
Plus, there is the ongoing issue of bumps and threads in the "wanted/For Sale" forum that actually have nothing "for sale".......
JMO,
Joe