I want to walk to Thailand on a one-way ticket because I'll be staying 2 or 3 months ... do they check .....

.... for onward or return reservations when you enter the country?

Is it absolutely necessary to own an onward or return flight out of Thailand to show the immigration officials?
Answers:   
Someone mentioned that you needa visa to grasp into the country. And the visa is only good for a fixed time period. I don't know how much difficulty you'd own in getting it extended, but I doubt that it's too much trouble.

I've traveled to many countries, and my airfare was never a factor surrounded by getting the visas. In fact, when I got the visas, I hadn't even bought the tickets yet. When I go through customs, they checked my passport for the visa stamp. That's all they cared about.
Having been to Thailand several times, you need a visa to stay that long, and you must prove you enjoy a round-trip ticket to get the visa. They do check at the airport as well!

Also beware checking your baggage to & from Don Muang -- stick to a carry-on pack, keep it under close watch or contained by your hands at all times, and never, never, never agree to "help someone out" by carrying something of theirs.
no, they don't check. many relations go to thailand without onward ticket. Bangkok is one of the great cities of the world to buy cheap airfare to... anywhere. that said, i ruminate it less than wise to go this opening if there is an alternative (such as a round trip ticket). 2-3 months is not a good reason for this.

best you find cheap discount round trip ticket. buy it "amenable ended." when ready to go, you nickname the airline a couple days in advance and confirm return flight. discount business fluctuates wildly. you may be standing here in bangkok ready to go and find it impossible to purchase return airfare for any sort of discount.

when i suggest "discount" i don't propose those supposedly discount sales on the internet. what i mean are small travel agencies (often chinese owned) that you find in NYC, LA, San Francisco, or Seattle that buy life-size blocs of deep discount tickets. (these are called bucket-shops). check major reporters in those cities, travel section. my last Seattle-Bangkok-Seattle ticket be under $650. there is no way i could own purchased one way tickets for this price; i checked.
One channel tickets usually mean you are on the run.
Did it ever occur to you that you may grasp to Thailand and never return? Do you know what can happen to "tourists"?

I would be very afraid. Hope you speak fluent Thai. Watch some of the movies about travelers to SouthEast Asia. Their jail are legendary. You don't have to do anything except be in the wrong place at the wrong time to home in one.
one way tickets are NOT a good conception because they would show that you did not intend to leave thailand - unless you have proof that you were disappearing by another method - train, boat, or private car. I don't know about Thailand specifically but most countries expect you to have a return ticket

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