There are a lot of companies that are not scams, but charge so much, sometimes more than the car is worth.
Most people put that money in the bank for when the car breaks down, just have a reliable mechanic who you can deal with locally and never the dealership and sign up with AAA or similar in case you need a tow.
One of the worst extended auto warranty companies is USfidelis, they originally quoted me $4700 for a vehicle with 40,000 miles on it and the warranty would be good till 100,000 miles. The thing is, there policy lists specific parts they cover so if your transmission died, they only cover specific parts, most of the time, the part you need fixed you have to pay for.
What i can tell you, look for a company with an A rating by BBB, a zero deductible policy, make sure they include towing and rental and ask them for a copy of the contract before you sign, if they lists parts, don't sign with them.
Depending on the age of the car and amount of mileage, your may be better off saving the cash to pay for the repairs outright.
If your vehicle is still under the manufacturer's warranty, see if the dealership has a policy that sometimes goes up to 150,000 miles. These policies may cost more, but as least you know the repair will get done properly.