Tourists can claim the 7% VAT back at the airport when they leave the country. The condisions specify that you must stay in Thailand less than 180 days in a calendar year to qualify for this. I stay in Thailand much longer on my Non-Imm B and work permit.

So do the customs officials at BKK airport enforce this rule? Any experiences?

Very easy to check if your in Thailand more then 180 days just by checking your passport why you file for your refund.