Something that is basically just deck (in the sense of this site) with two haves, think deck area as your trade and sideboard as what your trading for.
This would be more for in person trades and aid in fast look ups and using the same price database to calculate values.
It could also have a button for "trade complete" where it pulls from your inventory the cards your trading and puts in the new ones.

I dont think it should be alot on the programming side, just a new deck type kind of, but what do i know, I'm a bear i bite the heads off fish.