Did you talk to him and ask why he wants to bore it? Is it wear, clearance, bore finish, a whim? If he can't tell you what he found and why you need to spend the cash I would doubt his ability. If he knows, he should be able to tell you why and "sell" you on it. Be stupid. Keep asking until you understand. If he gets attitudy and says "trust me" then maybe think about finding a better shop.