plugin installation

I need a custom wordpress plugin built for my ecommerce site that will allow the users to be able to trade items they have for sale for items that someone else has for sale on their page. So its a plugin that allows 2 users to trade items they have for sale. The site in question is [login to view URL] and its a Buy Sell or Trade sit where the users list their items for sale for a fixed price, but then another user interested in someone else's item can invite that person to view the items they have for sale and maybe trade items they dont want for items they do want. then both users would be charged 1% of the value of the items they were both selling. so say i wanted your £100 iphone and you agreed to swap for my £100 leather jacket then we would both be charged 1% once both parties agree to the terms of the deal. So that basicaly what I need the plugin to do. thanks