Engine condition can be quickly triaged externally:
-Using the multiple functions of a manifold vacuum gauge (i.e. wandering/bouncing/low needle indicates different engine problems),
-Looking for burn marks on dipstick and oil cap,
-Looking for oil leaks underneath,
-Listening for bearing noise with a stethoscope probe,
-Read codes with an OBD2 scanner(there are hundreds of differing quality) $20
Amazon.com: U281 OBD2 OBDII CAN Auto Scanner Code Reader AirBag ABS Reset TooL VW Audi Skoda: MP3 Players & Accessories
-Back pressure tester at the tailpipe, $40
Tool Aid 33600 Exhaust Back Pressure Tester - Amazon.com
-Testing CO $220
Gunson Gastester Exhaust Gas Analyzer Tester | eBay.
Get a Carfax or other and check panel gaps and signs of respraying at the edges of panels.
Look at owner service records.
That's a start. The test tools are reusable or sellable.