Can I request a 30-day extension on my Thailand visa after 60 days without changing my return flight?

The user is planning to travel to Bangkok in May with a round trip ticket based on the US rule allowing a 60-day visa exemption, plus a request for an additional 30-day extension. They are seeking advice on whether this plan is feasible, especially since the return ticket is non-refundable. Community responses highlight that proof of onward travel may be required, the possibility of extending the stay is not guaranteed, and the return flight should be carefully timed according to the extension request. There are also suggestions for inexpensive flights to use as proof if needed.