Is it permissible to engage in a business venture where the profit margin is not fixed, fluctuating between 30% and 40% of the profits, and how can this issue be resolved with a partner who refuses to precisely define the percentage?

For a partnership to be valid, there must be an agreement on a known percentage of the profit, such as a quarter or 30%, because it is earned by stipulation. It is not permissible for one of the partners to be given a fixed amount of money. If the agreement is on 30% of the profit, then the partnership is valid. The merchant must inventory and calculate expenses to determine the profit and give you your share. His failure to do so raises suspicion and may be a circumvention; because making the profit a percentage of the capital invalidates the partnership. If your partner does not manage the capital and expenses, nor knows the amount of profit, and does not give everyone their due, then partnership with him is not permissible.