one quick way to assess condition is to remove the oil filler cap or dipstick. if either shows signs of varnish cooked on, that shows conventional ( cheaper) oil was used rather than the synthetic called for in most manuals.
ask for service records and see if services were performed regularly
modern motors will last a long time if taken care of.
my 2001 GMC w 4.8L has almost 170K and so far has only needed a water pump and a fuel pump..and synthetic oil and brand name filter about every 4000 miles.
transmission fluid/ filter changed at 100K
mike