Is it normal for customs to question frequent visitors to Thailand after multiple border runs and extensions?

You​ need​ a​ proper visa​ as​ you​ are​ not​ a​ tourist.​ At​ some​ stage​ you​ will​ get​ refused entry.

Immigration does not play around here in Thailand. Sounds like Mission Impossible to me and will self destruct maybe not in 5 sec but immigration will catch up with you. Who knows they could ban you for a few years or permanently IMHO

Unfortunately it is hard to say what will happen as it all depends on the Immigration Officer you encounter. Some people are lucky but like Brandon said there is a good chance they may send you packing.

Yes !!!! Use your other passport because your biometrics are different . 555

It’s not customs that pull you aside, it’s immigration

I suppose you were questioned in immigration and not in customs ?

Yeah, most likely will let you in one more time or deny you next time. Fly into BKK and pay for fast track service. Don’t fly into DMK they always grill people. 2x extensions is immediate reason for them to not allow you in the country with the current administration rules. Also dual passport won’t matter, your fingerprints got you unless you wear mission impossible style finger print covers

Don't rate your chances of getting through immigration

Good luck to your next trip back to Thailand. High chances you will be reject entry due to you have used most of your good luck of 2025.

You're not unlucky. You've outstayed your welcome as a tourist.

You're lucky you were not denied entry. Immigration no longer considers you a tourist as you're clearly living in Thailand. You're all but guaranteed to be pulled out of line next time and very possibly denied entry for trying to live in Thailand without a long term visa. They're currently denying entry to hundreds of people per week for abusing the system. You can find many reports of this across the internet and even in this exact group.

And entering on a different passport is going to raise even more red flags as when you scan your fingerprints they're going to see your entire record and assume you're trying to hide something by using a different passport.