From a friend in the wholesale/auction used car world: Now is not the time to buy a used car, rental or otherwwise. Because of the rental car industry dump of inventory, used car values across the country are about to take a major hit. The number of parked rental cars is STAGGERING. Toss Kelly Blue Book numbers in the trash bin for at least a year.
If you plan on holding it for a long time, you might get a pretty good deal versus buying new. Just don't plan on the used car being worth anything for a long while.
Caveat emptor.