I second everything that Hung says. My current airplane was a flight-school rental. Or, as the broker who sold it to me tried to spin it, "it's a one-owner airplane!"
It should get a good pre-buy inspection, just like with any aircraft purchase. However, a flight-school plane means it was getting a 100-hour inspection (the equivalent of an annual inspection) every hundred hours instead of just once a year.
Even so, these are trainers and may have seen their share of hard landings. So the pre-buy inspection should concentrate on the landing gear mountings in the belly and firewall in addition to the regular stuff. There are several 150s and 152s running around with over 10,000 hours on them and flying quite well.
