As a tourist, you are not required to pay Value Added Tax (VAT) on items more than 5,000 Baht that you intend to take out of Thailand. For most people the amount returned is very welcome and a pleasant surprise, so it is well worth making the effort to collect the paperwork you need for a refund. It is not that difficult to do either.
Stores participating in the refund scheme display a sign stating: "VAT Refund for Tourists". If you make a purchase from these stores, ask for a VAT Refund Form (P.P 10) and keep the original tax invoice(s) a store gives you.
That is really all you need to do. If you take that paperwork to the 'Customs Inspection for VAT Refund' desk at Bangkok, Chiang Mai, Hay Yai, Phuket or U-Tapao International Airports, you will be granted a tax refund. Bear in mind that the tax refund process is the final stage of your journey in Thailand - you will have gone through passport control on your return leg before you arrive at the appropriate counter. You can only make claims on the day you leave the country.
If your claim is for less than 30,000 Baht, you can receive a payment as a cheque or Bank Draft, or the amount can be paid into a credit card account. If your claim is for over 30,000 Baht, you can only receive payment by Bank Draft or payment into a credit card account.
For more information on VAT refund, visit the Revenue Department of Thailand's website: http://www.rd.go.th/vrt/howwill.html