I can see a lot of ideas to improve the 1 on 1 trading but one idea, that is pretty obvious, has not been suggested yet (AFAIK).
How about "my own" CS? You click my toon, and instead of selecting Trade, you get "Cons. Store". Then you get to browse the items I offer, at your own pace.
There would be no fees or limits in this personal CS, and the trade would be cancelled if I leave the zone. It would be nice to have indication like "Milanlameman is browsing your store" and "Milanlameman left your store". Or some icon could hang above people's head when they are browsing.

Of course you couldn't trade item for item in this but that makes a minority of trades, I believe.

It could be enhanced to buying too. I'm afraid it would require a lot of work from the developers, OTOH "requests" would make a nice addition to the regular CS:
You click item in CS, select "buy for", enter price, pay fee, tadaa, request listed.