Conformation Critique?

Not a fan of that hind end assembly at all. Can you get a photo of him actually standing normally?

He's back at the knees in front, too. That's a larger concern than the rear for a horse that will spend a lot of time under saddle.

If a seller can't be bothered to provide pictures and video as requested (within reason) then I would keep looking. The head placement isn't the concern as much as the rear being parked out behind. You can hide a lot of flaws with that pose.

I would actually pass him by for endurance/jumping on the forelegs alone, though.