FWIW I tend to only buy ex rental cars myself. I like the $avings on a fairly new veh. With that being said, as with any used car make sure to look it over really good. I know plenty of people who said they would never buy a rental car, and then later bought a used car and then found out it was a prior rental. All completely shocked, never thought rental cars could be "good" vehicles.
YES, go to a fleet auction and guaranteed you will see wrecked, smashed, been to heck and back rental cars and it is completely obvious what those cars have gone thru. Stay away from those. They are usually so ragged with broken parts and beat up interiors that they usually end up on sub prime car lots. Those are the junkers, cars that the manufacturer voided the warranty on because of damage.
If you buy a car directly from the rental agency, odds are that its one of their better units. They will gladly show you the maintenance record, sometimes without asking. Rental agencies have invested a lot of money into the disposal of their fleet, they want the best vehicles on their lot to help undo the stigma that rental cars are beat up pieces of junk.
There are so many ex rental cars driving around this country, agencies buy nearly a million cars every year, only to dump them after about 12 months. There of course will be people who say buying a rental is the worst idea ever, well good, more cars available for me
.