Personally no I would not do that unless I knew someone who knew the horse personally. But that is me.
This horse could turn out to be a maniac under saddle, or unbroken, or not the horse in the photos etc, if your ready for that possibility then yeah sure, go ahead.
But, if you choose to go ahead and you get a vet check, you choose the vet. Don't let the owner of the horse sway you into choosing a particular vet for any reason.
I've had things go seriously bad by letting the owner of the horse choose the vet who did the exam since I didn't know any in the area. Do your research on the vets in the area and chose one you like the sound of. Good luck :)
R.I.P ~ Bubbles - 25yo tb mare - 13.04.2011 ~ 8:30am ~ passed away naturally and peacefully in my arms