Is it permissible for the solicitor to take the price difference if he is able to provide electrical items at a lower price, after the company and the client have agreed on the initial price, knowing that the company's profit will be added to the quoted price? And is it permissible for him to take the same price as the contractor if he carries out the installation work himself outside working hours, knowing that it is not within his specialization and will cost him less?

It is not permissible for the project supervisor to request the finishing of his house at cost price from the executing company, because this falls under the category of bribery, winning favor, and favoritism in work. Gifts to workers have been considered an embezzlement (ghulul); therefore, the aforementioned contract is not valid. As for the questioner's work in performing installations for a fee outside his working hours, there is no harm in it, provided the company is informed and an agreement is reached with them.