Who decides, or who should I contact to find out if I would pass the ABC / Borello test as an independent contractor living in California under AB5?

You are definitely on the right track here. Being an independent business (either as a sole proprietor or partnership, or as a corporation or limited liability company) is an important factor in determining whether your business is really an independent contractor. If you choose to be an independent contractor, you can control the factors that would be used to determine whether you are an independent contractor. 1. Make your business "official" -- get a business license from your locality (city or county). Yes, it's a hassle, but it helps show that you are an independent business. This is true whether your business is a sole proprietorship, partnership, corporation, or LLC. Talk to your accountant and bookkeeper, as well as an attorney (if necessary), to see what would work best for you.  2. Have bank accounts in the name of the business, separate from your personal accounts, and make sure that proper bookkeeping is done for the business. Treat your business as a separate entity. If you withdraw cash from a business account for your personal needs, make sure that you treat that properly -- either as income, or perhaps as repayment of a loan you made to the business.  3. Have written contracts with your customers or clients.  Written contracts are good to show that your business is an independent business. You can write in the "ABC" test requirements into the contract, and that will go a long way to showing that you are a business. The contract can state that: A.  your business is responsible for getting the work done, and has the general right to determine how it is done; B. the work that your business will do is sufficiently different from the work of your client; and C. that your business customarily does this kind of work for other clients as well as this particular client.