like a section for people buying or selling full chars
or a section for people looking to upgrade a char but doesn't know what they want, or a area for a person tradign a single particular item that doens't belong to any category.
Then a section for people looking for a specific item.

That way people with whatever intentions they have will be able to find what they are looking for easier and there would be less bumping/spam and more topics would be able to be viewed and people won't be left out cuz a certain some1 with their object didn't see their thread ont he 2nd page.

I'm a D3 player and this is for an active game, which is what drove me to this reasoning.

That is what the filters and search are for, you can specify the items you're looking for and filter out the rest
If you're looking to upgrade and don't know what item is better, you should post in the discussion/strategy and guides section

there are filters? I didn't know there was such a thing. it isn't advertised very well