Not planning to do DIY. Saw a few Facebook advertisements today, for coating only cost few hundred ringgit haha dunno can trust or not

Example below

Using acid car shampoo for waterspot monthly is a bit extreme, also you dont mean those black lines right? it's the rain spot marks, right?

I'd say prevention is better than cure : I'd recommend using a decent spray sealant to protect & prevent stubborn waterspots rather than using acid car shampoo monthly.

I see. In the market currently these are the only 2 acidic car shampoo.

There is another option which is to use the common "Watermark Remover" product out there, it's much more affordable but it has it's risks as they are usually quite strong acid, you need to know what you're doing with it.

I still do strongly recommend aapply spray sealant on your coated car afterwards, it does help reduce stubborn waterspots and stains.