Its a possibility, because it would look suspicius. Cause say you sell the items for 500 platinum or 1000 platinum and your giving it back for a bronse mod to make it easy on yourselves. That trade back of the plat might be picked up as a suspicius trade based on their previous experiences and you both would be banned, plus the people that bought the items would loose the amount of plat used in the sales, making some of them go into negative. Best way is to have your friend do the trading them selves, but what you end up choosing is up to you.
NB: I don't know specifics and I don't know if it would be problematic or not. But this is based on what I have heard over the years.
xXDragonGodXx's post in Blocking a friend's account for trading was marked as the answer