The best way to learn about a driller is to ask other local bowlers who have used him, both in his home house and other houses around the area. Most good drillers will know about the conditions in their home house and in the neighboring houses as well.
In addition to talking with other bowlers, check out their bowling hand and look for tell-tale signs of ball fit problems. Many bowlers will swear their driller is the greatest and then when you look at their hand, you will see thumbs and fingers that are torn up by poorly fitted balls.
Feel free to discuss with a prospective driller any questions you may have, including what type of reaction you hope to get from the ball in a certain house. If he is truly knowledgable he will take the time and discuus whatever it is you want. Hopefully, the driller will be able to watch how you throw, so he can ascertain how to drill the ball to fit your game. Also, check to see if he will make any adjustments to the fit and surface after the purchase to fine-tune the reaction for you. (Since you didn't buy the ball in his shop, he will probably charge you for any surface change work.)
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"Beer is proof that God loves us and wants us to be happy." Ben Franklin
Enjoy,
Bob