I think the existing Ebay/CL/etc section and Classifieds are enough for Tom & the Mods to handle.
The way I see it, if I have something for sale and I get a reasonable offer, I'm OK.
The occasional goofball that offers 1/2 the going rate, I can ignore.
Either way, it's a comparatively small audience here, and the volume of eyeballs is the appeal of a worldwide auction site.