I don't use budget airlines. I fly frequently and want good service and reliability. All the airlines I use have flexible options in their fares to cater for people who may want to change their itinerary. Return fares are invariably cheaper than 2xSingle so I like to take advantage of that
I'm a regular traveller. Live in Thailand but spend 4-6 months per year travelling. I always have a return or onward flight booked. Get a flexible ticket with, for example, Singapore Airlines or Qatar, it's easy to change with no fees. I understand all airlines tell their customers to ensure they meet entry requirements of the destination country (and also transit).
Actually it is an immigration requirement although never enforced by immigration, but airline check-in staff don't know this, so they err on the side of caution. I think you'll find every airline has reference to it in their T&C
It'll be in their terms and conditions. It's your responsibility to ascertain if your destination country requires this (or even any countries you are transiting)
Yes! Interesting how so many 50+ expats complain bitterly when they encounter a small obstacle and threaten to go live in another country as if their leaving is going to leave the Thais distraught! Sometimes I do wonder how these guys made it through 50+ years of their lives! 😆