Hi Fed, I think technically you can. But like others have said, maybe after the
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/6th time they might ask you questions. I doubt that there is a visa for 10 days a month, so you fall into a grey area. You could ask your local Thai embassy the story seems perfectly acceptable it’s just wether an immigration officer might think you are here on “business” once a month?
To the group , if he gets 30 days on his first visit what happens when he comes back 20 days later ?