What should I do if I have a 12-hour overstay in Thailand before leaving?

If you have a 12-hour overstay in Thailand, there are generally no issues if you are flying out. Comments indicate that for overstays under 24 hours, immigration may waive the fine of 500 baht and simply annotate your exit stamp to note the overstay. It's recommended to confirm with immigration if you should pay the fine at the airport or beforehand, but often it's manageable without prior payment.