BRL,
A 'classified section' sounds like a great idea, BUT as most if not all of the Mods are working crew I don't see how you would have the time, energy or resources to control it..... setting up a payment mechanism would certainly bring in some money... but I don't think that's what you or we want. It's not what (IMHO) Pprune is about.
Leave the selling/buying to Ebay/pilotweb/flyer etc etc.