I think the only issue with the trailer delivery is if you are financing the car, as papers need to be signed.
You can do all that before. They just email you the papers and you print and sign and send them back.
Buying a car from a distance is no problem nowadays.
We live just outside Glasgow and collected the car from JCB Medway. Me and the good lady jumped a train for London about 6 in the morning. The salsmen were great, they picked us up from the local train station. Nothing was too much bother.
It seems like a drag going miles away to collect it but its like a kid on Christmas day just waiting to go downstairs and see if Santa has been. We stopped half way up the motorway for a nights stay and continued the next day.
The only problem with that (cue Monkeyhanger

) is to run it in on the motorway isn't the best for it but I was up and down the gears throughout the journey.
I don't think I'd want some stranger driving my car a few hundred of its first miles. Plus like others have said, if there is any kind of structural damage, paint etc that would be the supplying dealer that was responsible not a warranty claim as such. If a guy has just driven 200 miles and the car has a defect it will be another 200 back and 200 to be delivered again.
Trailer maybe.