I would say the one owner and full service history says an awful lot about how it's been cared for. If you're really interested juju get it inspected. 78,000 is nothing to modern engines. Also you have to think of how much mileage you're going to put on the car yourself. My Forfour is a 2004 and it's not done 30,000 yet. If you want a Brab get your skates on.
You should make sure you phone first. I found my wife's auto Tigra on Autotrader and it was seventy miles away. They said they'd hold the car till I got there to view. When I picked it up the following week they met me at the station. That was a one owner car and we still have it ten years on. Genuine 50,000 on the clock, used every day, and some would say that's worse treatment than high mileage use.
