Is it permissible to take money from the price of merchandise purchased for a hostess without her knowledge, in exchange for driving her there in a private car?

It is not permissible for a trustee to deduct a fee from the price of the merchandise, because he is a trustee, not a hired worker. He must render the trust to the one who entrusted him. There is no objection to the trustee requesting his fee for what he does or apologizing for some needs.