I would like to go one step further.
If the screw up was from negligence or error on the shop operators part, he should replace the ball (unless a slug would be acceptable to the customer) - at which point the drilling should be discounted, or at least no charge for the slug).
BUT - if the shop operator refused to make it right ON HIS ERROR, I would not only refuse to do business with him in the future, but I'd make sure and tell everyone about it!!!
Two related stories:
1. Several years ago my coach suggested going less reverse in my thumb to get me out of the ball quicker. I asked my pro shop guy to make the change on one ball. He refused. "I measured your hand and drilled that ball the way that is right for you. I will not change it just because some coach thinks he can fix something that way."
I have not been back since. I went to the guy I'm still using - he changed the pitch in one ball as I asked, and earned all my business since.
2. A friend of mine - a pretty decent bowler - went into a local pro shop a couple of weeks ago. He asked for an aggressive ball from one manufacturer. the guy drilled up another brand and type of ball. My friend felt obligated to pay for it - used it for less than 1 game, and sold the ball to me, for a significant loss. I maintain that he shouldn't have originally paid for the ball, and walked if the shop owner didn't make it right.
BTW - that's NOT the shop I use. I sent my friend to my guy.