I’ve visited the tax offices. Even the HQ on Ari. The officers can barely do the simple tax of Thais correctly. Anything foreign and they had to open a huge rule book to check and you think they are going to check which foreigner is filling his overseas income taxes and find the source of income ? AND PUT A PENALTY? They neither have the personnel or infrastructure to manage it. I think one should just avoid these taxes and just file the regular income taxes until it becomes a Visa essential requirement.. It’s just incorrect tax filing. With a penalty. The rules aren’t clear. Until they make it clear ,Not heresy. No need to be proactive about these taxes. I think most foreigners are just too paranoid of having their retirement visas revoked etc.
If you already had a work permit with one employer and that employer gave permission to you to freelance. You can literally report the income as well 😂 I even paid vat on my income when I was in Thailand from my part time gigs. Illegal working is bad. But there are some rules like attending conferences and lectures on the side which are exempt from work permit rules. So English teaching etc falls into one of those when done in the right and immigration stops being bothered. Different if you worked in anyone’s bar part time. You definitely will screwed . But yeah to err on the side of caution. Don’t do it. There’s more things that can go wrong than just that.