What is the ruling on the money my sister and the tailor receive from fabric shops in exchange for sending customers to them, knowing that the percentage was once fixed but is now unfixed?

It is permissible to act as an agent for fabric shops in exchange for a known fee or a percentage of the customer's purchases. This has been allowed by jurists, provided that the fee is known to avoid dispute, and that the agency is based on truthfulness and giving good counsel to customers.