Accidents happen more frequently than other countries, but not so much as to make it “likely”. However they are generally hideous and the only time I did it there were two families with their children, two of which were using plastic potties.
I have lived in Thailand for 10 years and have never been asked to show a departure flight at immigration. However I have been asked by the airline innumerable times and only last December I had to sign a waiver stating that I would pay for my own flight if I was refused entry into Thailand.