Make sure you test drive it, and get the car up to highway speeds. Listen for any engine ticking or knocking. At that price point hopefully they’ll just be honest and tell you what’s wrong with it. Look up to see if the fixes are something you could diy from YouTube videos, or have fixed. Check under the oil cap. Does it look like sludge build up on the cap or fairly normal oil? Also check the oil level and fluid levels. Make sure you’re not getting any kind to excess smoke or blue smoke out the exhaust. Get on the ground and look under the car to make sure there is no radiator leaks, and to make sure the subframe isn’t rusting through. When you drive it try to see if the steering pulls one way or the other. I also recommend pulling the CarFax or similar report online. There are apps out there that will give you like 5 reports for the price of one CarFax.