150,000 miles on a 6.7 wouldn't spook me in the least.
That - especially if the maintenance records speak well of the owner... Hopefully they also paid attention to the front end re: tie rod bushings and steering dampener.. Last - see if they'll let you drive it and get it warm enough to drop an oil sample and send off to Blackstone for an oil test.. If that comes back with a clean bill of health I think you'd have a good machine..
