Leon, I started a business very similar to cue building 30 years ago. I designed and fabricated. I rarely charged for design work, but quickly learned that it was absolutely necessary, especially for the wealthy, to get a sizable deposit. Most of the time 50%. Larger jobs less. Customers rarely would back out. Without a deposit even the wealthy can have buyers remorse or second thoughts when time comes to pay. If the customer backs out a portion of the deposit should apply to work done. A credit for a less expensive cue could be added to the contract. Even though you deal in many small commissions I would recommend a signed written proposal and or contract. All specs and details regarding payment should be included. Customers will not think less of you or feel they are not trusted. Most will think you are not only an excellent craftsman, but a good smart business man. Most artists and craftsmen may not agree, but that is why they are known as starving artists.
30 years later and I am still learning. Remember that to run your own business takes many talents. You are the bookkeeper and the janitor.
You do the marketing and sales and much more and if you find time may get to build a few cues. I do not wish to preach, but see an amazing potential for you in business and wish you all the best. When times get tough the competition is weeded out. Bob H. (Wanna Be Cue Builder)