Does dealing with an installment company, whose transactions most scholars do not permit, affect the freight company that collects the merchant's money from this company?

If the transaction between the merchant and the installment company is Islamically sound, then there is no objection to collecting the merchant's dues from the company. However, if the transaction between the merchant and the installment company is usurious and invalid, then it is not permissible to work on collecting the dues, due to the affirmation of falsehood and assisting in it therein.