I like to ask about the behaviors of the horse; like "is it like this often?" "what do you normally do when he acts up?" Questions that solicit an answer from the owner that might indicate that he'd like advice, or help. If you can try to 'personalize' what's going on, a person may be more willing to accept the advice. And perhaps you'd be able to even 'show' the person some things right there, that may help with the 'issue'.
It sounds like the horse just needs someone to teach him to not react in the manner he is reacting; ie, alot of desensitization, and ground work, to establish control and respect. He probably is genuinely scared, but because the 'authority' isn't there, is starting to act out, and running because it works, and gets him away from the scarey sounds, and objects. Maybe you could help the owner regain respect... I don't know that I would have told a stranger he needs to sell the horse right off the bat, when maybe he's just not had the direction he needs with this particular kind of situation. I would have wanted to work with him a few times in order to establish that he 'needed' to sell. The horse may have been okay when he got it, but is learnt to take advantage; he could be turned around again if he had the manners in the first place. I don't know, it's just alot to 'judge' from a first appearance, and interaction with a horse and owner.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."