All airlines are supposed to deny boarding if you don’t have an onward ticket. In reality, some agents do and some agents don’t. Personally, I’ve been asked and not been asked. I’ve also heard that some agents don’t accept an onward bus or train ticket. That doesn’t make sense, but it’s possible. Most people “rent” an onward ticket from onwardticket.com or one of their competitors. It’s a real ticket that is automatically cancelled the next day or two. $15US or so.

Your question cannot be answered without knowing which country's passport you hold.

@Robbie *****

Yup. They are real tickets that are automatically cancelled after a short period.

It’s likely, not 100%, you will be denied boarding without an onward ticket within the 60 day visa-exempt period. You should consider “renting” an onward ticket from onwardticket.com or one of their competitors. They are typically $15US and, if purchased just before you leave, are automatically cancelled after your flight.

I recommend you go to Immigration about 5 days before your visa-exempt stamp expires.

25K to 30K baht?

No problem leaving on the day your visa or visa exempt stamp expires.

Punctuation matters.

@Jonnie ******

He won’t be able to get an IDP with the required motorcycle endorsement because he doesn’t have a motorcycle license in the UK.