Like any cleaning, if the cloth is dirty it can leave smear marks on your window.
Your HOBOT 298 comes with a set of cleaning pads, but it is always a good idea to have some spare. Helping to ensure your windows will end up with the best possible clean by not having to reuse a dirty pad. The pads are washable and should be replaced every 6 months.
Price is for a set of 3 cleanig pads.