90k miles is only just getting started, my Jazz Hybrid went to 256k miles in 6.5 years, and had a hard life as a driving school car.
I think a minimum requirement would be a full service history, not necessarily a main dealer history. I am also a bit ocd about tyres, if the car has a good brand of tyres, I think its a good sign that its been looked after, if the tyres are a non-premium brand, where else has the owner saved money? Maybe that's just me?