- you can get a dummy ticket for free but apparently they can’t always be verified. The guy at the check-in desk actually typed in the reservation number to his computer, I assumed to verify it was a genuine ticket. 
I traveled to Bangkok 5 times in last 2 years each time with no onward/return ticket with various airlines. Starting destinations were London and once Barcelona. I was only asked to show a return once ( Etihad ) so I booked a dummy ticket on my phone ($16) while talking to the check in guy. Took about 2 mins, he waited for me to “find” my ticket.