How many visa runs can I do in Thailand with a tourist or visa-exempt status?

I used to do back-to-back visas. Never had a problem. Twice I was pulled aside and yelled at about staying long time in Thailand. I kissed butt and they let me through. As indicated previously, no limits by air, there are limits by land. Advantage of cross by land, if you get denied entry you can go back to a different border fairly easily. If you get denied at the airport you have to fly away someplace. You may not get to choose where they fly you to, could be; home country, where you came from, nearest country.

It's a risk to do back-to-back but I found the rewards were worth it.

my brother had 12 a year. going back and forth to Singapore for many years. if you look presentable and financially solid you should not have a problem

Technically no limit on entries other than 2 exempt land entries per calendar year. No limit by air.

That said if the officer thinks you may be trying to buck the system using tourist visa or exempt entries they will at some point pull you aside and question your intentions. They can also refuse entry.