*Update
Just crossed back over the Mae Sai border (30 days visa exempt). It took only a mater of minutes, and no questions asked. I had 25k I'm my pocket in case questions were raised, but it all went smoothly. I spent the night in Chiang Rai, but it's easy to do a same day trip from Bangkok if you wish to do so.
TLDR : Answer Summary
The user successfully crossed the Mae Sai border using a 30-day visa exemption, reporting a quick and hassle-free experience without being questioned. They also shared that it is possible to spend a night in Chiang Rai but emphasized that it can be done as a same-day trip from Bangkok.