Remember that if you buy something you are checking, you bring it to the airline to check in, they tag it and let you take it with you to the VAT desk, they stamp the form and they keep your checked bag and you then get your tax refund. That way they ensure that it's being taken out of the country.

If it's a carry on, you'll take it and go through security and customs, and then airside you'll take it to the VAT counter where you'll give them the form and they'll stamp it, and you're good to get the tax refund; this way they've verified that it's leaving the country as well. Yes, one could get around the system, I'm just pointing out how it works without the purchaser breaking the law.