Cars: Handling the deal after the deal

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NEW YORK (CNNMoney.com) -- You can spend hours negotiating the price of a new car, but even after you shake hands, the wheeling and dealing is far from over.

Once you're ushered into the a back office to sign the paperwork, the finance manager can make a compelling pitch for a lot of add-ons like insurance and protection that can give back a lot of what you saved.

But it's his job to sell. It's your job to decide what's worth your money. Here's how to make the right choices.

Dealerships can usually offer the best auto financing rates. Help yourself out, though, by checking your credit rating and arranging other financing before you go to the dealer. It gives you a fall-back plan and something to negotiate with. And remember, auto financing rates are not set in stone - you can bargain them down.

Don't take that car before you've got a signed financing deal in your hand. If the dealer says "Don't worry, we'll work out the details later," tell him you'll take the car later, too, and hold on to your trade-in. Otherwise, you could find yourself with a raw deal when it's too late to back out.

And read everything, word for word, before you sign.

"When you go to take delivery of a vehicle, take at least an hour out of your schedule," says Lauren Fix, author of the book "Lauren Fix's Guide to Loving Your Car."

If you don't have enough time to sit and read carefully, ask to take the papers home with you and come back later for the car, Fix advises. If the dealer says you have to sign and read the papers on the spot, take it as a bad sign and walk away.

Beyond financing, the finance manager will present various insurance, warranty and financial products.

"They all have value to the right person," insists Randy Brenckman, director of dealership operations for the National Automobile Dealer's Association. In particular, customers who plan keep a car for a an extremely long time may find value in some of these items.

But Lauren Fix and Phil Reed, consumer editor for the automotive Website Edmunds.com, are more doubtful about most of these offerings. Some may be worth it to a few customers, they agree, but very few.

Here's what they advise:

Protectants: These include rust-proofing, fabric protection and paint protection.

Rust isn't a big problem for most cars these days. Most vehicles already have long rust-through warranties.

Auto paint suppliers and car companies have teams of highly paid chemists working to make sure car colors last longer. If anything more could be done, it's probably been done before the car left the factory.

Finally, badly applied pant and rust protection can actually cause problems, so be careful.

Credit life insurance: Don't let a car dealer sell you life insurance just to cover your car loan. If you need life insurance, buy it from an insurance agent.

Gap insurance: Cars lose value fast, and insurance only pays what a car is worth, not what you paid for it. If your car is totaled or stolen while you still owe more money than it's worth, gap insurance pays the difference. If you've got a big car loan, it could be worth it, and it's often required when leasing a car.

But if your car loan's that big, that's a problem in itself. A smarter move is to pay as much as you can in cash - Reed advises at least 20 percent - to prevent this sort of situation from the get-go.

Extended warranties: This one's up to you, but make sure you know what you're buying and what you already have. Most cars today have long powertrain warranties. The powertrain - a car's engine and transmission - is where expensive problems would happen. But most powertrain warranties already last longer than most people own a new car.

Like everything else you buy, extended warranties are priced for profit. Odds are you'll end up spending more on the warranty than you would have spent on repairs. But some people just like knowing they have extra coverage.

Maintenance plans: Paying up front for a maintenance plan is a matter of personal choice. The biggest reason to get one is that an upfront payment gives you a give a big incentive to get that maintenance later, which could pay off in preserving the value of your car.

Theft protection products: Again, know what you already have. Most vehicles sold today have some sort of theft-protection system built in. Assuming the car is insured against theft, that's probably all you need.

Systems like LoJack, which use GPS to help locate your car after it's been stolen, may be worth it if you have a particularly valuable car, says Fix.

But it might only help you get back a trashed hulk when you would have been better off losing it and taking the insurance pay-out, says Reed.

Another hot seller is VIN etching. A technician etches your car's vehicle identification number into doors, windows, fenders and other parts that are commonly stripped from stolen cars and sold.

Decals let potential car thieves know the parts have been marked so they won't want to steal your car...in theory. But again - do you really want to get back the ripped-apart pieces of your car? Sometimes it's just better to say good-bye.