When renting a car at the airport, you are typically pressured to purchase insurance from the rental car company. The Columbus Dispatch has a very good article on what to look for, and what to avoid. My recommendation is to do your homework ahead of time and you can save a good deal of money.

When you rent a car, the scam you’re most likely to encounter is pressure to buy extra insurance.
Readers have asked whether sleazy rental agents target senior citizens. Not necessarily, but some agents do target renters who don’t know the ropes.
A basic rule is never to drive a rented car without two basic insurances: collision, which covers damage to the car you’re renting; and liability, which covers your financial responsibility if you hit someone else. Any other insurance you’re offered likely is to duplicate coverages.

The Columbus Dispatch - Travel.