Many small businesses gain free advertising by using forums.  An example is the Gun Connection (SC) owned by Craig V. Prince, who posts on many firearms forums as MAX100.  There are currently many upset individuals, including myself, who have given this individual money, and cannot get a refund or their product.  I'd like to pose the question, should moderators (Possibly even the owner of the forum itself) be held legally liable for losses incurred, when they allow positive reviews of products, made and sold by individuals such as this, but delete posts on the same topics which warn people not to give that business cash up front.  I have personally had this happen on the ShotgunWorld forum.

buyer beware

No.
Furthermore, such liability is legally prohibited by Federal law specifically Section 230 of the CDA.