I did similar last year; drive up from London to pick up a new XC60 near Stirling (but combined the trip with a stay with family in Scotland). It went really smoothly to be honest, get as many videos sent to you as you need and make sure they cover what’s important to you. The drive back down was much nicer!
I paid a refundable deposit of a couple of hundred then paid for the car in full once I’d driven it; certainly wouldn’t pay in full before you’ve had the chance to check it out in person.
Good luck
