bring a magnet along, and try to see kung makapal na yung masilya ng car, most probably it was involved in an accident. try also to knock the body, most well maintained bodies wud sound lata, while other na makapal yung masilya medyo dead na yung sound.

also, ive read this on FHM, try swiping ur fingers around the muffler tip (if u dont mind getting ur fingers dirty), if the deposit is quite greasy, the engine might not be well maintained.

try to test drive the car and look for weird noises on the suspension and the engine.