Do you honestly think a salesman cant see through that, they know every trick in the book.
Most salesmen may know every trick in the book but a lot of them do not have the power to offer discounts or even offer you a price on your trade in car before talking to their manager. I know of one dealership with 4-5 different brands of car that for all sales the twelve sales men make they must first run their offer via the manager.
So this means that they cannot even offer you a price on your car to be traded in without approval.