Anything used is a "take your chances"
If you can OK it with the owner, see if you can take it to your mechanic or garage and have them do an inspection on it. They will generally charge you about an hours labour but well worth it. Have them look at brakes, suspension, and all things safety related first. Then ask them to look for any accident damage, any leaks, condition of rad etc.
Look online and see if there is any common problems current and previous owners have experienced. Do your homework!
You may buy it and it might be the best car you ever had and then again.....it might be a nightmare.
I myself would look at Hondas and Toyotas! Very reliable cars and usually problem free for many many many miles!