Going against the delivery company’s stipulations with regard to the make and model of the car
Question

I know a man, a relative of mine, who works for apps, delivering orders; he is the one who delivers orders to people, such as food and other things. But some companies stipulate conditions, one of which is that the car should not be of lower quality than a certain model, or it should be of certain types. This relative goes against these two conditions, and he has not changed until now. I advised him that this is going against the conditions, and that is not permissible, and I said: your wealth that you earn from this work may be haram. But he was not convinced, and he says: The car is very good, and there is nothing wrong with it, and I am not doing anything wrong. I want a fatwa about what he is doing, and which explains how to get rid of this wealth if it is haram. Is what he is doing not permissible? And is that money haram?
Praise be to Allah.Firstly:
If the company stipulated that in order to work for them, the representative should have a car of a certain make and model, and he accepted that, then he must meet that condition, because Allah, may He be exalted, says (interpretation of the meaning): {O you who have believed, fulfill [all] contracts} [al-Ma’idah 5:1]. And the Prophet (blessings and peace of Allah be upon him) said: “The Muslims are bound by their conditions.” Narrated by Abu Dawud (3594); classed as sahih by al-Albani in Sahih Abi Dawud.
Al-Bayhaqi (14826) narrated that ‘Umar (may Allah be pleased with him) said: Rights are defined by stipulated conditions. Classed as sahih by al-Albani in al-Irwa’ (6/303).
In other words, the rights of each party to a contract are to be determined according to the conditions that they both stipulated. So the one who stipulates a condition for himself is bound by that condition, so he is obliged to fulfil what he stipulated."(Mawsu‘ah al-Qawa‘id al-Fiqhiyyah by Dr. Muhammad Sidqi Al Burno  10/809).
Going against those conditions is lying and cheating, both of which are haram. So if he claims that he is complying with the conditions when in fact he is not doing so, then he is a liar, and if he had the stipulated kind of car, then he replaced it with another car without the knowledge of the company, then he is cheating.
It was narrated that ‘Abdullah ibn Mas‘ud (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “And beware of lying, for lying leads to wickedness and wickedness leads to Hell. A man may continue to tell lies and endeavour to tell lies, until he is recorded with Allah as a liar.” Narrated by al-Bukhari (5743) and Muslim (2607).
Muslim (102) narrated from Abu Hurayrah that the Messenger of Allah (blessings and peace of Allah be upon him) said: “Whoever deceives is not of me.”
And he (blessings and peace of Allah be upon him) said: “Scheming and deceiving lead to the Fire.” Narrated by al-Bayhaqi in Shu‘ab al-Iman; classed as sahih by al-Albani in Sahih al-Jami‘.
Secondly:
The money that he earns is permissible for him, because it is in return for his efforts at work, although he has incurred sin by lying and cheating, and he must repent from that, by stopping work until he acquires a car that meets the conditions, or he informs the company about the car that he is using at present.
And Allah knows best.