Is it permissible to deal with a factory that takes a 10% commission from the marble installation fee, or a factory that increases the original installation price and takes the increase?

It is permissible for the manufacturer to agree with the customer to install marble at a certain price, then hire someone to do the installation at a lower price, with the profit being the difference. This is called "subcontracting" (ijarah min al-batin) and is permissible unless the customer stipulates that the manufacturer must perform the work himself. It is also permissible for the manufacturer to purchase materials, install them, and contract with another party to perform the work at a lower price. This is known as "parallel istisna'" (manufacturing contract), provided that the two contracts are independent. Furthermore, it is permissible for the manufacturer to direct the customer to the service provider in exchange for a commission, which is called "brokerage" (samsarah).