Or, in the trade box there could be a loan button where you decide how long you want to loan them an item, and they decide on a price to pay. So say you want to loan a savage set out for 3 hours and you want them to pay 100k, after the trade is completed there is a timer counting down, after the 3 hours is up the savage set is returned to the owner and the 100k is still with the owner of the savage set. I pretty much based this off the loan system in the game Runescape.