I used to work in rental. I did this for almost 3 years...one of the shadiest jobs I experienced. Here's a piece of info that is disturbing and why I would never buy a rental fleet vehicle: These cars aren't insured. In CA, if you have $35,000 to set aside with the DMV, you do not need insurance. Why is this the most scary part? Because if the rental car gets damaged, it will almost certainly not make it onto a Carfax report. Repairs are handled as an operating expense so an insurance claim on a damaged vehicle is never made...at least that's how it was done at Enterprise where I worked. We were "self-insured".
If the accidents don't scare you, consider what has already been mentioned. These are rentals. Even though they can cycle these out of the fleet within a year at relatively low miles, i.e. 1 year at 9,900 miles, these 9,900 miles could been split up by anywhere between 100 (conservative estimate) to 200 (aggressive estimate) renters over the course of that one year. Not all will treat this car like their own. Even rental employees took the opportunity to "test drive" these vehicles. Maybe 80 out of the 100 babied the rental, but then you can only imagine what the remaining 20 would've done.
Here's another little known rental tidbit that nobody talks about: Maintenance. We were required to follow a generic maintenance schedule. At the time, oil changes were every 3,000 miles. There were times when either the car was out on a long-term rental, or if rental branches were really busy during the week that these cars didn't always make their maintenance schedule. For some cars this is OK because scheduled maintenance as per owners' manual allowed it to go past 3,000 miles, but this is not the case for every car.
Personally, knowing what I know, I would never buy a car from a rental fleet...or probably any fleet for that matter.
if you do find yourself in a position where you have to buy one, you will need to ask the right questions:
1) Request accident history - What repairs were made to the car. What's difficult about it is that you have to take the rental companies' word here and there is no source for you to validate their answers.
2) Request maintenance history - Rental companies keep accurate records with regards to maintenance. They should easily be able to provide it to you. Compare the maintenance intervals to a factory maintenance schedule for that particular car. You can find an owners manual for almost every common late model car online nowadays.
2012 Mustang GT, Ingot Silver, 6M, 3.73, Brembo.
Whipple 2.9, Flowmaster AT Cat Back 817500.