There is no legal obligation to share your receipts, cost structure, etc. with any customer or other person, except and only to the extent you had agreed (such as in a contract) to do so.If he will not pay you, the most straightforward thing to do is to sue him for the money for breach of contract--for failing to pay the amount he agreed to pay. If the amount at issue is less than the maximum for your state's small claims courts, you're probably best off suing him in small claims, acting as your own attorney (if the business is not an LLC or corporation--if it is, you will need an attorney, even in small claims). If it's more than that, retain a lawyer to help you.