Praise be to Allah.
You say that you are in charge of accounts, preparing and equipping, and that buying the apartment came under the heading of equipping. Based on that, the work that you did is part of the work for which you are paid a salary, so you do not have the right to take anything from either the buyer or the broker, because this comes under the heading of what is called “gifts to workers”, which is haraam wealth.
The Prophet (blessings and peace of Allah be upon him) appointed a man in charge of collecting zakaah. When he came he said: This is for you, and this was given to me. The Messenger of Allaah (blessings and peace of Allah be upon him) stood up on the minbar and praised and glorified Allaah, and said: “What is the matter with a worker whom I send, and he comes and says, ‘This is for you and this was given to me’? Why doesn’t he sit in the house of his father or the house of his mother and see if he is given anything or not?”
Narrated by al-Bukhaari (7174) and Muslim (1832).
Al-Nawawi (may Allah have mercy on him) said: In this hadeeth we see that gifts to workers are haraam, because it is a betrayal of his position and what has been entrusted to him. In the same hadeeth, the Prophet (blessings and peace of Allaah be upon him) explained the reason why gifts to workers are haraam: it is because the worker is only given that gift because of his position. So it is not like a gift to someone other than the worker, because such gifts are mustahabb. The ruling on that which is taken by a worker and the like in the name of it being a gift is that it should be returned to the giver, and if he refuses (to take it back) it should be added to the bayt al-maal. End quote.
Based on this, if you took something from the buyer or broker, you have to give it back to him.
For more information, please see the answer to question no. 87864.