Yes, bizarrely, Thai border pass holders can visit those islands on the same pass that they use to access Kawthaung but foreigners basically need a visa to visit any island now (except maybe Grand Andaman, where the casino has closed). This despite your visa not being checked when you get on your boat at the Kawthaung jetty.
On a marriage visa. They will ask on any visa (not extension of stay) unless you use a visa run service. Now I did use Saphan Pla best to use one of the other piers, which are the dedicated ones for the various tour companies as those are better.
I talked my way out of the requirements, but that's because I am an assertive, fluent Thai speaker.
On a DTV? Poipet is a bit dodgy, but one guy on here stated he was denied re-entry on the Thai side on a DTV despite being in Cambodia and Vietnam for 3 weeks.
Avoid that border for re-entry to Thailand. For departure, no issues at all.
The only possible exception is if you're driving a vehicle and YOU must be the driver, since passengers have to stamp in, in the dreaded arrivals hall in Aranyaprathet.
Poipet on the Cambodian side is no issue but the Thai side often does deny entry randomly. Only the vehicle entry point is relatively OK but to be absolutely safe, re-enter elsewhere, there are 6 other international border crossings.
The other requirements such as a ticket out of the country and/or lodging are not as important as the
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Baht in cash. I talked my way out of it (I did have almost 20K in cash to pay for my expenses in Myanmar, which is basically cash only) and I was surprised they would ask a marriage visa holder for this. Finally they stopped and again, it was asked for upon exit. Upon re-entry, no issues as I was already vetted.
They ask because they need to ensure you can come back and they know you're trapped there. I was there last year. They ask when you leave. They even hassle you if you present a Myanmar visa and explain you're going to the islands for several days.
It depends what you want to do. It is necessary to get out on the islands. Not necessary for a quick turnaround in Kawthaung, which is what 99% of farang do.
Yes that's what I said. You can only stay in Kawthaung and surrounds. Even some of the islands require a visa, whereas Thais can use border passes even for the islands.