Forms of leniency in buying and selling

Question:
I have a friend who sells me cars, and sometimes he leaves me with a portion of their value, forgiving me for it. Is it permissible for me to take this money?

Answer:
There is no harm in that if you have a dealer who sells you cars, or other items, and he forgives you for some of the cost; because you deal with him; and because you buy a lot from him; so there is nothing wrong, there is no harm in this money; because this is a type of gift from him, and assistance from him; because you dealt with him, or because you are his friend.
As for if it is on behalf of others, you are an agent for people, an agent for an organization from which you buy; because he gives you a discount, so you leave the appropriate price that suits your clients for the sake of the fact that this one gives you, and the other does not give you this, this is not permissible, this is betrayal—seeking refuge in Allah—some people are agents who look for the people who give them [discounts], and buy from them at a price higher than what other people sell for; because they do not give them like those others, this is not permissible, he has no right to take anything from this seller; because this leads to him pursuing his own need, and not acting for the benefit of the one who appointed him.
So he must fear Allah, and buy from the people he sees that their selling is appropriate, and that it is good for the one who appointed him, and that it is from the trust, and advice to his client, to buy from these people, not for the sake that they give him money that is written in the sale, and he does not give it to them, he says: the sale is for one hundred, but you see that you only have eighty, the twenty is for me, this is injustice, and betrayal of his clients, we ask Allah for safety.