Get a VAT receipt when you buy the camera. I imagine a back-street place doesn't do it but the "higher-end" should. THEN, when you go through immigration there should be a place to reclaim it (I think in BKK it is outside immigration but this was a long time ago). It was sign-posted VAT Refubd. Take the article and the receipt and claim your refund there. In CNX it is (or was) in the international departure lounge. Google it - like I did - look for sign in the shop saying VAT refund for Tourists.