Many shops get balls with pins and tops "close enough" and make the drilling fit for people off the street. This may be "good enough" for the average person. However, it may not be the best it can be for that person. The shops don't want to deal with sending the ball back because it was not quite what they wanted. If the shops keep accepting something different from what was requested, the suppliers will keep sending you what they have in stock. It may or may not be what was ordered. It gets the balls out of the suppliers inventory and they won't get stuck with odd pins and tops. The shop will get stuck with them.
I do custom work for high average bowlers. (I drill only on request. I am not doing this to make a living.) The balls I ordered are for people who bowl high average leagues with brackets. Not carrying a corner pin or a short count in game due to the ball not quite having the right reaction made a difference in $. One of the bowlers is going to the US Open. I am confident he will make the first cut. The question is will he make the top 24. A "close enough" reaction is not good enough.
I eventually got the balls from another online shop. They specifically noted to visually check the pins on the instructions to their shipping department/supplier. The balls I received met my requirements. Both of the bowlers who receive these balls are putting up numbers.