Is it permissible for a company to take a known percentage of the profits from a person's trade, who is under its sponsorship, in exchange for its services to him?

There is no objection to taking a fee for services that are not in the nature of a guarantee, provided that the fee is known, and that it is not a percentage of the business profits due to the uncertainty thereof. Rather, the service should be known, and the fee for it should be known.