Oil pressure sensor inop, I'm my case the gauge read of the scale with ignition on. Sub woofer cutting out and OE Bose headunit skips CD's. Leaking rocker cover gaskets, checking previous service invoices and cost of spark plugs is a good indication of how it was looked after. If the plugs are cheap, it's more than likely corners may have been cut along the way also.
Ideally you want matching tyres all round and a decent name also gives an idea of how it's been looked after. Along with the above posts, the rest of issues are general wear and tear or clutch, brakes, exhaust, tyres and battery.