Very interesting idea. It might be my own perception of people but the words Trade Up might be taken by the public that you'd give full retail value on the old piece, which would be something to avoid. The words Trade In might not convey the same message, perhaps making a lower trade in value more palletable to the customer, because you haven't given them a false impression. Low price by itself is not the way to go for an independant, but this idea of yours allows the customer to use the residual value of their old piece. You are reinforcing the concept of value. You just need to be careful on your low margin items.