I've been questioned a few times by airline staff, and maybe once by Thai immigration. When spending thousands of dollars to travel around the World, I'm a: "It's better to have and not need..." type of guy. So, on one trip where it may have been an issue, I booked a cheap flight to Cambodia and actually went to Cambodia for an enjoyable few days.
Assuming your over 50 you can get a 90 day visa, or the regular 60 day visa. 30 days probably too short to set up retirement visa. Just opening a bank account can be difficult.
One of the biggest mistakes I see foreigners do in Thailand, is brag about their money. If the subject comes up, I always say I'm a broke "Cheap Charley."