It's a very cool idea, though I think it would be difficult to implement cleanly, given how complex some transactions get.
There are some groups like this world though, which would be useful to revive perhaps!
I don't know if this is possible, or pointless due to the forums and the existence of the commerce forums, but I feel like if a marketplace tab or section of the site existed (like Forums but just for selling characters), it'd make selling / trading a lot more easier and stream-lined.
The way I was thinking of it was a tab of itself which has a list of images of characters, how much they're being sold for, or what they're being traded for, etc. and then who is selling them / who created the species. That way you wouldn't have to open up say something like a thread to see what the character looks like.
This would also allow like in the example below for users to search up characters being sold by a specific user, or characters under a certain amount of $ or DA Points.
Here's a visual example of what I was thinking of from an online game, but of course replace these items with character images:
Let me know if I'm just being stupid or if this idea is pointless, but I thought I'd throw it out there.