What is the ruling on working in a company where favoritism is shown to some clients over others, and one is unable to discuss this with the manager?

It is not obligatory to be just and equitable among customers in treatment. It is permissible to favor some over others, as long as it does not infringe upon anyone's rights or wrongfully consume their wealth. Reducing the price for one customer or giving them special attention is not considered injustice to others.