My '05 PT Cruiser has the 10/100k warranty by default.
Gap coverage would protect you if you drove it home and totaled it the next day and the insurance only covered a percentage of your loan payoff.
If you owe $20,000 on your car and it’s only worth $12,000, the gap coverage might be worth it. If you’re only flipped by a thousand or two, the gap coverage will cost more than that and it’s not worth it.
If you have had an opportunity to hear Click and Clack, the Tappet brothers (Tom and Ray Magliozzi) on Car Talk on NPR, you’ve heard this as one of the many cannards they love to ridicule. When people ask them about undercoating, they just laugh their asses off. I’m sure they’ve never even been sued when they call it a rip-off and a scam. It’s totally unneeded. xo C.
There was a time when aftermarket rustproofing was a useful thing if done correctly and you lived in the rust belt, but that time has past. Regardless, I doubt it was ever your best option to have it done by the dealer at the time of sale.
No. Is it worth it? 
Ooh! I love it!
Nah, car dealers know the tricks, they aren’t going to be flumoxed by something like that. That’s not the way to get a great deal. Instead, do your homework, know what you are willing to spend, and be prepared to walk.
Always be suspicious of extras.
If they push hard, be REALLY suspicious. After all, why would they push really hard if it was a good deal for you? Dealers make money on repairs, too.
Just assume that everything a car salesman says is suspect, and you’re pretty much on the money. Always leave and come back another day, no matter how interested you are. They hate this because they know you might not come back. While you are gone, do research. Run the numbers yourself, too. They hate well informed consumers, too – salesmen often will amusingly sputter and get enraged when you know bluebook values and other things you learned on the 'net. You’re not supposed to have a fair chance, dammit!
Be willing to walk at any time. I know you might love the car, but would you love getting soaked on the deal?
Don’t buy in to acting. If you know you are offering a fair deal and they say “no way”, say “Ok, thanks for your time” and start to leave. 99% of the time, they’ll stop you and explain that the “manager” has to approve this sort of thing, blah blah, and take your deal if it really is fair.
This advice is especially important if you’re a woman. I had all kinds of pressure to take this, that, and the other thing when I bought a car as a 23 year old woman. They really put it on with the “I can’t believe my manager took the deal!” and “CONGRATULATIONS!! You were approved!” on the financing. Whatever.
Yes, it is. One of the scenes involves dickering over uncoating or some such thing. Not important to the story, but perhaps to character development.
Emphasis on the walk part – the last car I bought, the salesman wouldn’t budge on the last $500 we wanted him to drop, so we (me, the missus, and my Dad) hiked out of the dealership. We were halfway into our car before the guy came out and agreed to see things our way.