What is the ruling on money acquired from a percentage rebate given to the buyer by the selling company, and does the ruling differ if the percentage is given by the buyer or by the owner of the company?

It is permissible for the employee to take the money given by the company if it is separate from the purchase price and authorized by the ministry. However, if it is added to the purchase price, it is not permissible, due to the deception, embezzlement of public funds, and bribery involved. As for the money paid by you: if it is for transportation and labor expenses authorized by the ministry, then it is permissible. But if it is bribes to employees to achieve something false or to obtain what is not deserved, then it is unlawful, based on the Prophet's (peace and blessings be upon him) saying: "The curse of Allah is upon the briber and the bribed." However, if the bribe is to achieve a right that cannot be obtained without it, then paying it is permissible. And you have the right to claim the authorized expenses that you paid on behalf of the ministry.