Things to know when buying an ex-rental fleet vehicle?

I just found out about a rental company in L.A. that is apparently selling 3 or 4 used 2000/2001 ex-rental insights that have around 50,000mi, so I am going to be hunting these for a while. I also have a friend that works for Enterprise Rentacar in their Midwest Regional Corporate office, so I will be checking with him about possibly finding a used rental fleet insight through him.

Does anyone know any specific things to look for when buying an ex-rental fleet vehicle? Besides just saying it is generally a bad idea! My friend that works for Enterprise has bought 3 ex-rental fleet vehicles well below the market rate for those cars and he has not had a single problem with any of them! (albiet he gets the pick of the litter as he works for them!)

Any specific information would be greatly welcomed, I have purchased (or been involved in purchasing) several used cars and I know what generally to look for in a used car. But if anyone knows anything about ex-rental fleet vehicles that may be specific to that market, or if anyone has any general experiences buying ex-rental fleet vehicles they would like to share please feel free!