I bet they are just using some cheap stuffs to do it thats why still got water stain.
Btw how much paid? RM100 just wait watermark remover?
Waxco how much?

Rain X are not permanent, also its not a watermark remover. It just apply a layer of "oil" on the glass so it will repel water. Once the layer is gone then watermark will show again.
Plus it actually attracts dirt to stick on the glass so need to clean it even frequently