No more than about 100 miles.
If I am going to travel that far I will grill the person on the phone about the car beforehand 😆 That way when I go and look at it, hopefully I will have a fair bit of information about the faults and problems
The way I look at it is, car sales is a bit of a game where most people/dealers try and hide the cars issues. I will try to find them out before leaving the house so I don’t waste a journey. Some people are totally honest but they are in the minority.
I do this in a cheery cheeky sort of way and try and get clues about the seller.
Ideally i’d rather drive 30 minutes to look at a car and then if it’s no good, it’s no big deal.