Yes they can. But if you stick to the rules they have no reason to and wont.

I have had 2 setvs from hanoi and 1 from hcmc, alternating, in the last 10 months. Never even a question.

As of yesterday entering on a SETV i will be here 1 year on exemptions and setv. Never even a question. I am not working and always have proof of funds.

It's nice when things run smoothly.

Some people do have a year out in thailand as a tourist. Totally legit.

I have been here almost a year on tourist visas. I have never had an issue obtaining them or reentering. Just stick to the rules you will be fine.

There are too many efficient airports to count. Bangkok's airports have been rated some of the lowest in customer satisfaction surveys in recent years. Google it. As Thailands government has recently stated, they are trying to attract wealthier tourists instead of trying to increase the current numbers of annual visitors. Making people wait hours at customs is not a great start in sending this message out to the world. I think the OP has every right to be irritated at having to wait hours. It's a rational response. I am not sure he needs to be told to relax though. He seemed perfectly calm to me. I for one am grateful to people sharing their experiences here. We all should be.

I wasn't aware they did that at Don Muang. Nice info thanks Sean.

Sorry to hear that mate. I had the same happen before. Now I pay the premium and never flying into Don Muang.

Thanks for this. I have 2 stamps and 2 SETVs all extendes, i want to be here a year. I was worried about my next entrance, but like you said if your not breaking the rules...