When the consumer of a product is the (co-)owner of the “Physical Sources” (Means of Production), and accepts the product itself as the return on investment, then the price they pay as a consumer is exactly the costs they paid as a (co-)owner, and so profit does not exist because the final transaction (buying the product) does not occur.

If a group of people own a fleet of taxis because they want taxi service, then they must pay all the costs of operation, including any wages for work they do not take upon themselves, but they cannot pay profit, for who would they pay it to?