I have never ever been asked in Thailand for either money or return ticket, only time I have ever been asked is in Vietnam when I was flying back to Thailand from Danang by the checking in agent.
I was asked for the first time two weeks ago in Vietnam. Never over stayed or even extended. Been to LOS maybe 50+ times never any issues. Not sure If this was an over zealous girl or they’re getting strict. Or because I’d been in Thailand for a day before Vietnam.
I flew in to Chiang Mai from DaNang a couple of weeks ago and the Air Asia girl insisted on seeing my return flight out of Thailand. When I asked her what that had to do with her and she should concentrate on weighing my suitcase she wasnt going to give me a boarding pass until I showed her.