a lot of digital nomads don't pay taxes because they don't live in 1 place long enough but they enjoy the infrastructure that the taxpayers of that country provide.
From what I understand, only non B visa (work visa) will have custom exempt. There is Samsung factory here so replacing your TV and fridge is very cheap.
I'm registered with my country's embassy in Thailand so they know I am here. In case of emergencies that needs evacuation like war etc or death, they will contact my immediate family back home. If your home embassy has such service, it makes sense to do so.
Did you have proof of revenue and income to show them? Just having an online business doesn't prove income. Present your invoices and revenue stream and tax documents maybe?
The soft power activity must be Thai specific and the school or gym must be approved for DTV application. Don’t think Badminton is a Thai sport. So maybe that’s why you were rejected?