Trade prices

OK, so I am running Perch standard and need to add a trade price and a retail price per item. The trade price is for logged in members only. I can successully add and show/hide the trade price according to whether the user is logged in or not. The issue is when the item is added to the cart - the retail price is shown and calculated in the total, not my trade price. How do I make sure the trade price is sent to the cart, not the retail price?