The plus side of regulars offloading gear to other regulars is both parties are familiar w/each other and the exchange has a greater degree of trust and integrity to the gear than buying of an auction site or classified ads site.
But in the spirit of the site, the main focus is on sharing work, ideas, techniques, etc. Cluttering the main forum with for sale posts detracts from that...
Perhaps a sub suction like the "Articles" section would suffice if the admins feel the effort is worth it.