2 hours ago, Boedog said:

I have beeen going to Thailand for years and only o ce was l asked to prove l had a return ticket and that was the Thai embassy in WA because l was apply for a 6 month visa which they don't do anymore, on every other occasion flying into Bangkok not once was ever asked to show return ticket, just go to immigration and get an extension 1900baht can take a few hours so get there first thing, someone there will help you fill out form

The rules are very clear: if entering visa exempt, proof of onward travel is required.

Many countries require, depending on the type of visa, a return or onwards flight booking.

Few countries check every passenger to see if they have met that requirement. Airline staff at check-in will be more likely to ask for it as they can incur penalties if they transport passengers without the required documentation. 

If you are one of the people chosen to produce such ticket at check in or passport control there's no point citing precedence as an excuse for failing to meet the requirement.