Always buy rustproofing, if you bought a car crappy enough that the paint job doesn't include anti-rust elements, especially if you live in a location with lots of water-based weather or near the coast.
Why are you adding money to the lowest price they can sell at? That is your target price -- the lowest price they can sell will always be the lowest price that includes a profit (or the smallest loss, for brands like Chevy). Besides, most of the profit comes from the optional packages, which are marked up 200-500%.
ah, but never buy rustproofing (or optional alarm, tint, etc.) from the dealer! those are the optional extras that are marked up 200-500%. there are specialty shops that will do the same exact thing for much cheaper.
also, every modern car sold today has anti-corrosion measures, as well as corrosion warranties, so i don't see why you would pay extra for rustproofing. this might've been a good idea 20 years ago, but i don't think it's necessary today.
There was for a time a program on UK TV (BBC) called something like "Don't get done, get Dom!". They'd use an earpiece to send people in to buy cars, he'd be listening via hidden mic and would tell them what to say / do. He was awesome.
He'd get the "best price" and then tell the buyer to say, "that includes the mats and metallic paint, yes" (or similar). Basically the guy thinks he's secured it, you hit him for that last bit.
He did a general buying show too.
Re the article - not all dealers are equal: You come back at 4pm, the cheapest dealer has had the alloys switched off or put on cheaper tyres (that's £50 at least). You've no time to go back to the others. You buy? If you don't do you think the other dealers will play your game the next day or just see you as a time-waster?
Why are you adding money to the lowest price they can sell at? That is your target price -- the lowest price they can sell will always be the lowest price that includes a profit (or the smallest loss, for brands like Chevy). Besides, most of the profit comes from the optional packages, which are marked up 200-500%.