All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
If both the company and the client agree beforehand on the amount and method of maintenance and on the fees, and they agree on that, and the maintenance is performed as required, then the charged fees are lawful, whether large or small. Also, it is permissible to work in this company.
However, the technicians should make reasonable profit from the cost of their work, so as to make their service accessible to their clients without burdening them financially. In doing so, they will be characterized by leniency in dealings, as Muslims should be. Likewise, they will expose themselves to the Mercy of Allaah, The Almighty, because the Prophet, sallallaahu ‘alayhi wa sallam, said: “May Allaah have mercy upon a man who is easygoing when he buys, when he sells and when he asks for payment.” [Al-Bukhari]
Allaah Knows best.