Is a return flight or onward ticket required for a 90-day non-O retirement visa in Thailand?

When arriving in Thailand on a 90-day non-O retirement visa, there are differing opinions on the requirement for a return flight or onward ticket. Generally, non-immigrant visas, which include the non-O retirement visa, are exempt from the onward ticket requirement, as the main purpose of these visas is to allow individuals to stay and reside in Thailand. However, some airlines may still insist on having a return or onward ticket for boarding, regardless of the visa type.