Thailand cracks down on tourists who stay longer than 90 days without a proper visa. However, if you buy a 90-day tourist visa, there's no problem; you just have to pay
This is perfectly in line with the rules in Thailand.You can't enter more than twice, with a maximum of 90 days each time, which makes 180 days in total. After that, you'll need to get a 90-day tourist visa, which you'll have to pay for.
That's not exactly how it works; they can go back two or three years to see the number of visa runs you've done and the total number of days spent in Thailand.