What is the ruling on working as a real estate marketer for residential units sold on installment, knowing that the sales contracts include a penalty clause for late payment on the buyer, and this condition is usurious and forbidden?

Imposing a financial penalty on the buyer for delays in paying their due debt installments is usury (riba) and forbidden.

This is based on the resolution of the Islamic Fiqh Academy, which states: "If the debtor buyer delays in paying the installments beyond the agreed-upon date, it is not permissible to obligate them to any increase in the debt, whether with a prior condition or without one; because that is forbidden usury."

The questioner's work in real estate marketing is not deemed unlawful due to the presence of such a condition, because their work is unrelated to the usurious condition and does not involve direct assistance in it. Rather, it is limited to a permissible aspect in itself, and the sin of the usurious condition remains with those who stipulated it and acted upon it.