Is there a sin incurred by one who stays in an expensive hotel, the costs of which were paid by a work colleague, knowing that this will not affect the performance of governmental work?

If the director of the consulting office paid for the hotel due to your professional position, then this is a forbidden gift for an employee that must be returned. There is no sin upon you for staying there if you return the amount to him. However, if the payment was out of a desire for reward or due to a previous friendship and normal gift-giving, then this is a praiseworthy gift. The distinction between the two is made clear by the hadith (definition) of Ibn Al-Lutbiyyah, where the Prophet, peace and blessings be upon him, said: "Gifts to officials are ill-gotten gains," and he encouraged the official to sit in his father's or mother's house to see if he would still be given gifts or not.