I have never been checked. I read somewhere they only check if, you volunteer, they've been tipped, you're obviously bringing in more than your quota (6 gold watch, 1 wrist). I don't know how true it is. The only time I have seen people getting check are those people who travel with 12 suite case, ( I didn't say Indian, I am sure other people do it too)
That happens sometimes. For me once or twice a year. I have started transfers that said a few seconds, later I get an email that says a few days. I started a new transfer the next day for the same amount, got within a few seconds, the original transfer finally came through after a few days.
I don't know my longest run, I have a few long term visas (marriage, work, volunteer). I have had several back-to-back tourist visas. I don't think I have ever had a visa exempt. I have been here 9 years. They really don't seem to care too much. I have been question twice while coming in (once by land, once by air). Both times the Immigration Officer made comments like "next time you come back...", they knew I am a habitual tourist.
I think the trick is just to not be a jerk (Swiss).
I often wondered if you have to study Thai. If you can here to study English, then the test would be real easy and you wouldn't have to worry about getting the boot.
bus tickets.. It's "onward travel" not "onward flight". The last time I did this, I bought tickets from Hat Yai to penang, 12go.asia, it was like $12/USD, That was a couple of years ago (pre covid), the prices might have gone up some.