I totally agree that it would have to have strict guidelines.
The way I was looking at doing it is doing a generic listing of what I have, not an itemized listing, and tell peeps to PM me with their wishlist and I'd PM them back with what I have. An example would be, I'd list brand names of GPS units I have and tell peeps to PM me with models they'd be interested in and then I'd message them back and let them know what I have on their list, or alternatives if I don't have what they're looking for, then we can work out trading or price.
I think it can work but I don't know if Peter wants to open that can of worms?
Ribbit
Ps: I just sold a Garmin NUVI 780 to a really good friend yesterday for $100. See if you can find it on Ebay for that price?

I always cut friends a better deal than "strangers" I don't know.