Thanks for the suggestion. We're in the works of revising the rules in the For Sale section to help minimize these negative posts. Ideally, it is up to the buyer to do their research on any product they are interested in purchasing to reach an informed conclusion. The 'Classified Feedback' section is available to assist in this research.
The "For Sale" section is not necessarily a "Bargain Basement Pricing" section. Some members may be looking to make their money back, or perhaps make a profit---there is nothing wrong with this. Everyone needs food on the table. It is up to the buyer to decide if the price is reasonable for them.
Additionally, the "Report Post"

option is available. If you find any posts that are hindering your credibility, or the item you're selling, without reason... then use this icon to notify the moderators so we can clean it up. That's what we're here for.
Keep the comments/suggestions coming...
Justin