What could you gain? Sometimes you can use them as leverage if you (or the dealer) really want to move the vehicle sitting in front of you, rather than waiting for another one to come by that's optioned the way you want. You could say something like "I really like this vehicle, but I really don't want to pay the extra $500 for that (accessory)." and then follow that with either a "Can you take it off and remove the $500 charge?" or "I guess I'll visit (other dealer) and see if they have the vehicle configured without it". The dealer would try to follow up with "well, let's get you one configured just the way you like" if they have the inventory, but if they don't, and knowing they can't just "take it off", their options are either to let you walk away from a sale, or negotiate down the equivalent cost, e.g. throw them in for free.