Kitty,
I am so glad that you got a better rate for your car rental.
Regarding damage waiver or insurance, rental car company won't ask you to buy over the phone. When you pick up the car, they will ask you to "buy" for the proper coverage, since you cann't drive without an insurance on the rental car. Usually rental car company does not buy insurance for their cars.(Trust me, I work for a car rental company, not National though.) If you don't have a gold/platimum credit card that has damage waiver on rental, or if your own car insurance won't be able to cover a rental vehicle, you HAVE to buy it from the rental agent. The rental car insurance might cost you from $15-$25 PER DAY!!!!. It does add up. If you decline the damage waiver, and you don't have other form of insurance, if the rental car is damaged, you are liable for the whole repair cost....100%%
So, the bottom line it, ask your car rental agent about insurance (whether you need it,) make sure what type of coverage is provided by your credit card company as well as your own car insurance. Once you know what you are covered for, you won't be surprised by the extra insurance charges.....