In such a situation, saying "thank you" is payment enough.
*** When the person on the receiving end can't repay the kindness and feels compelled to feel appreciative, he or she can become extremely frustrated. Acting out can occur.***
It never bothered my worthless brother-in-law (If you know him he probably owes you money). He even took his own mother to the cleaners several times promising to pay her back but never has.