Yep, I can see the usecase for this and sounds like a reasonable requirement.
It needs some work on the technical side though... Right now we estimate the trade value by taking into consideration user's first 500 cards in their wishlist sorted by value, since those are the most relevant for this calculation generally. Looking at the possible intersections of uses with very big wishlists (tens of thousands of cards), with the tradelists of all other 60000 users on the website is not an easy query to make.
I do want to solve this problem, but it's not trivial or quick to solve . I did pay a freelancer consultant when I implemented the trading oppportunities to help with things, and will possibly do this again, but sadly right now there are no funds nor time. Hopefully in a few months time.