I went today to Mae Sai to renew my 'visa on arrival/exemption': Very smooth, very fast, no questions asked. The whole process (border crossing and return) took less than 15 minutes. The immigration officer even gave me a smile :-). Thanks you 'thai visa advice' for information. (to save money in the future, bring $10 for Myanmar visa, otherwise it is 500 Baht). Bus ride with greenbus smooth also: left CM at 8am, back to Chiang Mai at 8pm.
TLDR : Answer Summary
The user successfully shared their experience renewing a 'visa on arrival' at Mae Sai, noting the process was quick and efficient, taking less than 15 minutes with no questions from the immigration officer. They appreciated the smile from the officer and provided a tip to bring $10 for a Myanmar visa to save money, instead of paying 500 Baht. Their bus ride with Greenbus from Chiang Mai was also smooth.