Except you aren't going to be able to teach them anything if they balls aren't drilled to their hand. Teaching someone how to bowl using house balls isn't going to help them at all and in fact frustrate them because we all know it's about the ball "holding" onto you (and your thumb more specifically) then you holding onto the ball.
At the end of the day the single most important item in bowling is a custom fitted bowling ball, everything else is secondary.
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