I too am self employed - I took a sabbatical in Thailand 2 years ago on an METV. If you are self employed you just need to show a tax return rather than an employer’s letter.
My understanding is that they won’t let you out at Mai Sai if they aren’t going to let you back in again, as you can’t get out the other side unless you have a Myanmar visa. Otherwise there would be a weird Farang camp in the market of stranded people 😂.
If you have any worries and you don’t mind a day trip to Hull, you can email them all of your paperwork for them to check prior to going to get your visa. I’d definitely do this again when I get my next one as it takes a lot of worry away.
I purchased the cheapest flight I could find with a date of the 6 month point and used that for my METV application as I didn’t know what my travel plans would be then.
Tiger is probably a good place to start in terms of asking the ED visa questions - they are the most commercial of the Muay Thai schools on Phuket and are pretty good at getting back to emails.
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