Is it permissible for shop owners to ask for money in exchange for hospitality, and is it obligatory to pay the full amount if requested?

If it is customary to offer hospitality and no price is mentioned, the host has no right to demand money, as there is no sale; rather, it is a gift and a donation. If the giver says, "I have made you the owner of it," and does not mention any compensation, and there is no indication thereof, then it is a gift. If they dispute, and the giver says, "It is a loan," and the recipient says, "It is a gift," then the statement of the recipient is accepted, that it is a gift. And offering food is permission to eat, so no payment is required to the host.