Here's my opinion, for what it's worth: once you sell (or trade) something and it leaves your hands, you've made the exchange and that's that. Free market. But it's up to both parties to uphold the integrity transaction, no misrepresentations.
Something completely different is the spirit of this forum, which is one in which people make those exchanges because they're interested in growing figs. I've asked one person who didn't advertise to see if he could sell me some cuttings. It's just not in my nature to solicit anything without an indication of the item being available, but he said yes, at any rate - seemingly because he knows I have an interest in growing that particular fig. I've also bought from other members who did advertise. I'm interested in growing the figs they advertised as well as using the forum as an educational tool. By far and away, I've learned more than I've bought on this forum and I don't think those two sides will ever match one another. I will learn more here than I buy.
On the flip side of the buyer/seller agreement, a generous member read one of my posts asking for more information and sent a PM about a trade. He's going out of his way on a long trip to stop at my house with his end of the bargain. That's a person who's passionate about figs and this community.
I also believe that once you build up a currency of distrust among a community, you'll back yourself out of it naturally. No matter what, everyone should do what they think is best in terms of buying and selling, but as for this forum itself, maybe it's best to think of it as a meeting house as opposed to an auction house? That way, everyone can be heard, but maybe they'll speak their peace in such a way that respects everyone else?
I think I just rambled. I didn't mean this as shot at anyone in particular. But I like this forum, so I felt like saying it.