A couple more tips.
Never refuse to drill a ball the way the customer wants it. If you measure him at a 4" span and he says it doesn't feel right, he wants 4 3/4", explain the drawbacks and dangers of a span that long, but if he still wants it that way, drill it for him. If you talk him into using the 4" span and he doesn't shoot 750 out of the box, he'll tell people you messed his ball up and that he's never going to let you do any work for him again.
A customer comes in and buys a ball. You take him out to the lane, watch him bowl and measure his PAP. Then you go back to the shop and he says he wants the #3 drill pattern, and you agree that it fits his game well. You carefully lay it out and drill it per the specs. You take it out to him, he takes one look and says that it doesn't look anything like the picture on the drill sheet, and he doesn't want it. It's impossible to explain that the picture is based on a 5 1/2" X 1/2" PAP and his is 4" X 1 1/2". This actually happened to me and his complaints to other bowlers hurt my business. Now after I lay a ball out I draw the holes on the surface of the ball with a layout pencil and show it to the customer to get his approval before I drill it. -- JohnP