So I know we've all seen the craigslist ad's where they price their item (pin) from things they've seen on eBay.
Do you have a sentence or two that you say in an email that can tell the seller that basing off eBay is not necessarily true? You could be looking for a Gorgar but when you see it on craigslist and it reads "this pin sell for $3499 on eBay...." then you have a challenge in front of you to try to get it for $700.00. This can make the seller not want to talk to you. That's a big price difference,
Do you just walk away from the deal and monitor the ad until they realize it's not going to sell?
perhaps sending some eBay closed auctions may give you ammo to support your case?
-Rev