Oh boy, this is becoming a right pain in the sphincter

I don't know whether to go for low mileage, high mileage, newer cars, older cars or any other cars in that case lol.
I am looking around everywhere and what I see to be good cars are bags of sh!te.
The guy with the black golf reckons that around town he averages 25 mpg at best and obviously less when putting foot down.
What could be the problem as the car is standard with no mods