Definitely get a Carfax
http://www.carfax.com/ report on the vehicle before you buy it. You'll need to get the VIN number. I helped a buddies company out buying a used work van. We would get the VIN's and run them, WOW! Some the van's had possible rolled back odometers, been in wrecks, one flood victim van and one van that had been repo'd about 14 times.
Carfax will also tell you if the vehcile was serviced at places like Midas or a dealership. When we signed up at Carfax it was something $39 for two months with unlimited running of VIN's.