Def worth a look, suspect the issues may be a little deeper than they let on, otherwise why are they getting rid of him? But could be the rider just doesn't have the patience to deal with it. However remember he is older so doubtful he will change too dramatically, so if you can deal with buddy sourness, jigging, etc then go for it
The ad said they would let him go on a trial basis, so you can always do that. Just set up a contract. =] I think he is REALLY cute. Being barn sour could be a pretty easy fix, and he's an Arab, it's very typical of him to "jig."