It is hard to say. He seems to have scope. May work find for you. Why are they selling him?
That being said, there is a quite large difference between a 3 foot horse and a 3'6" horse. Those that can do the first well may not do the second well or hold up doing 3'6".
There is something about the outside of a horse that is good for the inside of a man. ~Winston Churchill
) Dinosaur Horse Trainer