If he's a certified driller and proves to have knowledge of bowling, why not try one? If you like what the guy talks about and what he does when he drills for you, then I say go for it. Sure, you might not get the same warranty and such as a normal pro shop might give you, but aren't new balls on warranty with the ball company anyway? If something goes bad with the ball, take it up with the company. Now you'll have the downtime between when the company can deal with you, but in my experience, I've never had that problem, so I'd give them a try.
And if he screws up, well you saved the money. Go get it plugged/redrilled at your normal guy and never go there again.
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---Ryan