Inner Adab of receiving a favor from the creation:

The inner rules which govern those who take from the hands of created beings:

The important and indispensable thing, when receiving anything from the hand of a created being, is to do so with both knowledge and courtesy [adab], both inward and outward.

Outward knowledge implies that you must accept only that which is acceptable in the Shariah, while inward knowledge implies that you take nothing, when possessing enough, except with the intention of giving it away; and accept nothing that your ego expectantly desires. 

The meaning of 'expectant desire' here is hoping and hankering after something from a particular source. Suppressing this is part of inner courtesy, to conform to which is a virtue. 

The obligation connected to inward knowledge is to know with certainty that the real giver is God the Exalted, for He is the One Who gave to the one who gave to you, commanded him to give, and will reward him with what is nobler and finer than what he gave. He is the One Who cast in his heart the irresistible urges which he could not countermand, made the act of giving pleasant to him, made [the thought of] you occur to his mind, and inspired him with the thought that there was goodness and benefit in doing you a favour; while [in reality] he did a favour only to himself. 

Now, tell me, can one perceive created beings, or abide with them, as long as one has this particular knowledge of God? 

Nonetheless, never fail to thank those who render you a service; be kind to them and pray for them, for He has commanded us to do so.
He only made them the instruments of benevolent acts, locations for goodness, mediators between Him and His servants, because it pleased Him that this be theirs, and it pleases Him that they be treated accordingly. When you thank them, you are in reality thanking God.

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From- Gifts for the Seeker of IMAM AL-HADDAD