I opened my SCB easy online account many months ago, I even asked the staff regarding the 'no withholding tax' stuff but alas last month, I had a 15% tax deducted from my account.
So SCB staff really don't know what is going on, they even assured me many times that my tax will not be deducted when I opened my account.
The incompetency in Thailand is astonishing, different people will tell us different things.