With eBay auctions it would mean copying every listing whenever you want to sell something, only ‘buy nows’ would last any time as a valid link whilst unsold
As a matter of a seller opting to list on eBay and refer to it on here rather than classifieds the seller would be losing 10% in fess on an eBay sale rather than a fee-less classifieds sale
(There are occasionaly fee-less direct links that eBay gives for people to share links)
If you highlighted your eBay sale then generated a forum sale you could avoid fees by canceling on eBay, but then you attract attention getting potential strikes against your eBay account
Members could post up their seller IDs and then people could look at what they are currently listing - I buy & sell random things, but as I’m not going to auctions at the moment I don’t think too many members would be interested in my suit and corset
If there’s a majorly exciting find that someone spots (but don’t fancy for themselves) they can post about it somewhere appropriate