Seems like the IO is just using that rule to stop people entering Thailand whom they suspect of working , will not effect non suspected working bonafide tourists
How do you spot the difference?
Tell tell signs .
Doing visa runs sometimes overstaying by a few days , sometimes understaying by a few days and always doing visa runs at the week-ends .
Under 35 and been in Thailand a long time , facebook page showing them in school ,quite easy to spot