Many countries in the world as long as Thailand require to show proof of onward travel. In simple words, they want you to show a ticket out to leave the country when the visa ends. And that's in order to avoid people to stay illegally in the country without jobs/money.

We come with the perfect product for everyone who wants to keep their travel fixable. fake return ticket for thailand for free! 

Is proof of onward travel needed to enter Thailand?

Yes. 

What would happen If I come to the airport without a return ticket?

If officer doesn't do his job you might pass. however, the likely scanrio is that he asks you to provider proof of onward travel (return ticket) to enter the country. If you don't have he will deny your entry and you lose your ticket! 

Thailand is amazing country with for shopping and flawless beaches with white sands.