@Kool ******
You need to spend more time reading some of the posts on these forums before giving out wrong advise. You are correct on that lots of people are allowed to board planes with either no ticket out or ones over their initial entry allowance. Most of those will be short haul trips from around South East Asia. However when talking about long haul flights it’s a different story. Legally immigration could refuse you entry (they rarely would) and because of that it’s the airline’s responsibility to return you back to where you came from. Many many times people are refused boarding unless they have a ticket out of Thailand within the initial allowance of days.
Saying “you’ll be fine” is just wrong. You might be fine, but then again you might well not be and better to be prepared beforehand with either a visa for the correct number of days, a changeable ticket or a a cheap throwaway ticket out.