How many times can I re-enter Thailand with a tourist visa before being denied entry?

It is kind of "you never know what," and depends somewhat on the quality and politeness of your response. The first time I was (unexpectedly) challenged at the airport, I truthfully told the officer that I was actively seeking local work, and the officer proceeded to suggest a couple of good places to apply and let me in. (I will save my other stories for later, as I, too, am seeking a more appropriate visa status for now...)

It also makes a difference if you are flying back, or doing a land border crossing, and how long you spent in the other country.

Quick question, are you registered as staying at the same address the whole time? I wonder if that gets alerted.

Its all up to immigration. I did it for 15 years and eventually told me i need get proper visa

5 years ago I had immigration at phuket airport ask why I had so many entries. Had 6 at that point and was told cant have more than 6 per year. With my work I had to do visa runs quite often. But normally they are quite easy going if you are polite.

A tourist visa is a single entry visa. Once you enter Thailand it's used up (no re-entry) and you'll be stamped in for 60 days which you can extend for another 30 days.

You can go to a neighboring country and apply for another tourist visa after that if you want. You'd again get 60+30 days.

There is no written rule that limits how many times you can do this.

But tourist visas are not for living in Thailand. Probably by the 3rd time you try to do this back to back, either the embassy is going to start asking you why you're living in Thailand without the correct visa and deny your application, or passport control when you enter the country is going to ask the same things and possibly deny you entry.

It's possible that you could do it without any issues for a year. It's not something to rely on though because a tourist does not live in a country for 6+ months.