There is a rule of business transaction – if one avails any kind of service or buys a product he has to pay the value as demanded by the seller in exchange of the product/service he bought to be called a rightful owner of it. Failing, it would be considered as if he has wrongfully robbed the seller without paying him the dues. And the product/service which he has so availed could be taken back from him in such a case.
“(Allah only desires to keep away the uncleanness from you, O Ahlulbait ! and to purify you a (thorough) purifying.)”
(‘Say: I do not ask of you any reward for it but love for my near relatives’)