Is it permissible to pay a commission to a buyer who threatens to deal with a competitor if he doesn't receive it, knowing that I am responsible for the sales department in the company?

A broker is someone who mediates between the seller and the buyer to complete a sale, guiding the buyer to the goods and the seller to the prices. There is no objection to the broker taking a commission from both parties or one of them, according to custom or agreement. It does not matter if he acts as an agent for the buyer in the sales contract. Based on this, it is permissible to give this person a commission for his mediation, provided that the owner of the company or his representative approves.