that is a good idea, however they will only decline/call you back if you have a decent trade in. With a decent trade you can probably get 19k on the selling price, because they will make that back up when they sell your trade-in. But honestly, dont expect them to drop too much below about 19,500 if your trade has no resale value (i.e. old, beat up, etc.)

If you can get about 20,500 out the door (after TTL) then you would be getting a darn good deal at a loss to the dealer.