Butterzone, I think where we agree is that not all critical posts in the marketplace or other areas where people are engaged in professional activities here are accurate or warranted. People who engage in such activity should not be free to do so without repercussion. Being critical of a user for engaging in actual fraudulent or dishonest activity is one thing, and users are free to bring light to anyone engaged in these acts pretty much on the entire forum. For the rest of the dedicated users operating here professionally and obeying posting guidelines, allowing this kind of activity or furthermore punishing users for acting against it is a slap in the face. Letting some one control their own marketplace thread does not some how silence critics because they have the ENTIRE FORUM to be critical of users. Not letting some one take a crap all over your storefront is not equivalent to silencing free speech.
Unless you own the property that someone is making speaking on, then you do not have any right to "punish" them for what they say. You do not own the thread in which you are selling your goods, and therefore you do not have any right to punish anyone who says anything in your thread (provided they are not attempting to scam).
It is a valid question to ask why you are charging a certain price when others are charging a lower price. If you feel your price is appropriate then you should respond to then why they are appropriate and any potential customer can see both of your arguments in a transparent way.