What is considered good mileage in a used car?
35 mpg Hwy is acceptable. 40 is not unusual. Under 30 mpg Hwy, it probably has a bigger engine than you really need.
10 to 15 thousand miles per year of the age of the vehicle. Example: on a 4 year old vehicle 40,000 to 60,000 miles on it is good. HTH. -Jim