The positives: You will likely be able to review the maintenance records of a particular car to check for troubling trends. If you can't look at the records, I'd be suspicious. And being that it's a rental, it has likely had regular, per-the-manual servicing. The vehicles usually have popular options such as automatic transmissions and decent stereos. You probably won't find any with manual transmissions and wind-up windows. Prices are usually set at a fair level, and there is a minimum of haggling. Some companies welcome trade-ins, others don't. Some may offer a limited warranty, or can help with financing.
The negatives: Many agencies are keeping cars a lot longer than they used to. I've rented some cars with more than 40,000 miles on the odometer, unheard of 10 years ago. The cars frequently bounce from city to city, and consequently the car probably hasn't been monitored for long by one mechanic. The car may have done service up north where salt was used on the roads. While prices are usually fair, there are few genuine bargains. Mostly, though, it's a rental. I treat my rental cars pretty well, but I know some people who don't. And I certainly don't treat them as kindly as a car I own. Plus, when you go to sell or trade the car, a title search will probably show that it was a fleet car in another life, and that can lower resale value.
