I don't see a problem posting a link to an item just to do a "price check". Granted most of us have picked up gear for little or nothing over the ages, but that will not last as stuff gets harder to find and people are willing to pay some money for them. Just like any other hobby posting final sale prices is a good idea to show members what is common, rare, and commands money (atleast so they do not toss it). I would also think people mine this site to see what we deem worth paying for.

Ebay only keeps concluded auctions online for a short time anyway, after which the links do not work.

As II2II pointed out, you cannot regulate attitudes. If somebody wants to poke fun at an ebay seller there are many ways around posting a direct link to it.