I think the guy is Australian so cannot enter Vietnam without a visa BEFORE he travels and that take at least 4 to 5 working days and $25 US dollars to get not to mention cost of airfare and time...
Visa extension is only around $50 US dollars and a couple a hours
Interesting that you don't consider bribery of immigration officers abusing the system..
If these people attempted to enter through these borders solo several times each year without the assistance of an agency bribing immigration they would have been rejected a long time ago.
But if you are confident nothing will ever change and this will just go on forever then good luck 👍
There is a fine line between a genuine tourist and someone abusing the visa exemption entries..
I would suggest if you are doing more than 1 border run per year to remain in Thailand then you start to appear not to be a genuine tourist and someone trying stay longer the typical tourist would.