She is a tailor and tells her customers to buy from certain shops in return for a percentage
Question

                My sister works for a tailor. She and the tailor agreed with some cloth shops to send customers to buy from them for commission. Initially this commission was fixed, then they unfixed it, but it is nearly the same. Is this commission halal?.
Praise be to Allah.
    There is nothing wrong with telling people to go to certain 
    fabric shops in return for a certain fee or a certain percentage of what the 
    customers buy from these shops. The fuqaha’ regarded it as permissible to 
    accept payment for acting as a middleman or broker, and there is nothing 
    wrong with it being a percentage of the price of the goods sold. 

    It says in Fataawa al-Lajnah al-Daa’imah (13/131): It 
    is permissible for the middleman to accept a payment of a certain percentage 
    of the price for which the product is sold in return for telling customers 
    about it. The middleman may take his payment from the seller or the buyer 
    according to the agreement, so long as there is no unfairness or harm. End 
    quote. 

    See also the answer to question no.
    45726. 

    It is not permissible for the payment to be unknown, so as to 
    avoid dispute between your sister and the shop owners, if they give her less 
    than she thinks she deserves, unless your sister wants to tell people about 
    stores without any payment, and the shop owner wants to reward her for what 
    she did voluntarily; then he may give her whatever he wants. 

    In order for this transaction to be permissible in the first 
    place, there must be sincerity and honesty towards the customers. It is not 
    permissible to send them to these stores if she knows that the same fabric 
    is available in other stores for a cheaper price, or there is better fabric 
    for the same price. 

    And Allaah knows best.