FWIW I'm a member of a photography forum that does that - there's a corner of the front page with a few specials on it that links to a bigger price list. Buying from the site is mostly cheaper than ebay and simpler, plus of course the seller is guaranteed. The site gets a small cut and everyone is happy. People still discuss other sellers and so on, it doesn't seem to have had any chilling effect.
The other thing about
www.dslrusers.com is that it has an image critique section that actually works. People give honest, constructive feedback and there are relatively few ego posts (because, well, if you whine about getting critiques people laugh at you)