The spectre of airlines and onward tickets raises it's head again.
Although it's not explicitly Visa-related, it can affect all of us to a greater or lesser degree.
All airlines use a reference book called TIMATIC, which contains all entry requirements for all countries. A new edition appears every month.
Airlines are obliged to follow the rules laid down by each country - failure to do so may result in the airline losing money and the passenger being deported back from whence they came.
Some of the language in TIMATIC is very precise ("passengers without proof of onward travel and sufficient funds WILL be deported). Sometimes it's less precise ("passengers without proof of onward travel MAY be deported).
When I'm called to decide if someone is allowed to travel, I'm at an advantage with Thailand as I know it well from personal experience and know full well that a 30 day extension is perfectly possible once there - for other countries I may spend 10 or 15 minutes reading through the rules .
I have travelled to Thailand many many times over the last 25 years. I have never yet been asked to show anything more than my passport - but I have always had my onward ticket and my hotel booking to hand. In recent years I've taken to carrying the required cash (THB 20,000 equivalent) as they're tightening up.
Just because you've not been asked before, doesn't mean you'll not be asked next time (doubly so if you're doing back-to-back visa exempts).
Please contact your airline if you have any doubts. The staff will do their best to advise you (though the call centres aren't airport staff and might not know all the relevant info right away).
TLDR : Answer Summary
The post discusses the importance of having onward travel proof and sufficient funds when traveling to Thailand, as per airline regulations influenced by TIMATIC, a reference book for entry requirements. It emphasizes that airlines are mandated to enforce these rules to avoid penalties and potential deportation for passengers. The author shares personal experiences and advice regarding documentation and suggests that travelers should be prepared with necessary proof, especially for ongoing travel arrangements.
