You already took his money. He is probably going to remain very unhappy with your presence anywhere. So if you make trouble for him, do you think
a) he'll take it "lying down"?
and
b) why will all his customers believe you, a stranger, when they have been going to him for years?
Unless there's no other driller for miles, there's no one to corroborate whther you're right or wrong. (You're probably right, but what difference would it make, if you made enemies and not converts. This is almost a "religious" matter.)
On the other hand, unless you're a driller, where are you going to get your new balls drilled?
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"None are so blind as those who will not see."