The most profit in almost any field is in accessories. For bowling it is inserts, tools, and other like items. Many tools used for bowling aren't bowling specific. They can be found in other fields for less. Some items are bowling specific and there for easily controlled on price.
Look at quarter scales. It's a cheap piece of plastic that sells for $50 plus all day. Look at what is charged for the color kits used in ball plugging. I would bet it's something that could easily be found at HobbyLobby for far less if you knew weather to get oil base or water base.
Working in a retail electronics store for a year really opens up your eyes to where the profit is.
