I'm in the car business and I currently work at our family dealership. I have worked in the finance department and sold extended warranties.
1.Rental car companies sell their cars directly through customers and through dealers. Dealers will buy them (example- we're a Cadillac Dealer and we buy program CTS and then we certify them to get the 100,000/6 year warranty) and resell them at less than what Avis, Hertz, etc will. Compare prices!
2. Extended warranties can be purchased if the car is still under the original factory warranty. EXAMPLE: Subaru is a 3/36K- 3 years OR 36,000 miles from in service date (date the car was first purchased- NOT Title/registration date). The seller will have this date or get the vin and call the service department of a dealer and they can provide this.
3. NON factory warranties are cheaper but not always better. Always check the dealer too. Apples to Apples might not be possible with a non factory warranty. Most factory warranties provide other things- trip interruption (breaks down while you are on a trip and they cover the cost of the hotel), rental car, etc. Call and ask the dealer to match the price you got. A good finance person would rather make $100 than NOTHING.
Good luck! Just remember...car dealers/sales people are only trying to do their job too. Be an educated buyer and the sales people/managers will appreciate it.
We aren't out there to try and take advantage of people but we do have bills to pay too and deserve to make a living at it. I know I'll get blasted for that comment but it's the truth!