I don't know anybody who has ever claimed that refund but here are some details:
When you see a 'VAT Refund for Tourists' sign, you can receive a 7% refund of the VAT levied on goods at the shop. Even so, certain conditions apply, and you won't be able to claim your refund until you depart Thailand from an international airport.
How to claim a VAT Refund
Goods must be purchased from stores displaying the 'VAT Refund For Tourists' sign. VAT refunds only apply to goods taken out of Thailand within 60 days from the date of purchase.
Goods must have a value of at least 5,000 baht (including VAT), and single purchases must have a value of at least 2,000 baht per day.
On the day of purchase, present your passport and request the sales assistant at the store to complete the VAT Refund Application for Tourists form (P.P.10) and attach the original tax invoice to the form. Each application form must show the value of goods of 2,000 baht or more.
Before departure, present your goods and VAT Refund Application for Tourists form to Customs officers for inspection before check-in. Luxury goods, such as jewellery, gold ornaments, watches, glasses, or pens must once more be inspected by the Revenue officers at the VAT Refund Office at the departure lounge.
You can present your claim to the Revenue officers, mail it back to the Revenue Department of Thailand, or drop it into the box in front of the VAT Refund Office.
Refund fees
For cash refunds, there's a fee of 100 baht. For bank draft refund, a few 100 baht plus a draft issuing fee at the rate charged by banks plus postage fees. For credit to credit card account refund, it's a few 100 baht plus a money transfer fee at a rate charged by banks and postal fees.
Refund conditions
Refunds will not be granted in the following cases:
You carry a diplomatic passport and reside in Thailand.
You are an airline crew member departing Thailand on duty.
Your stay in Thailand exceeds 180 days in a calendar year.
Goods were not taken out of Thailand within 60 days after the date of purchase.
You didn't depart Thailand from an international airport.
Name or passport number not on original tax invoice attached to the VAT Refund Application form
Value of goods purchased is less than 2,000 baht per day per store.
Your purchased items fall under the following category: gemstones, firearms or explosives, prohibited items
VAT Refund Application for Tourist form was not prepared on the date of purchase.
The total value of goods claimed for refund is less than 5,000 baht.
Original tax invoices were not attached to the VAT Refund for Tourist form.
You did not carry the goods out of Thailand on the day of your departure.
Goods were not purchased from participating shops in the VAT Refund for Tourists Scheme.
Quantity of goods shown in the VAT Refund Application for Tourist form is less than that shown in the original tax invoice.
Goods were taken out of Thailand without being inspected by Customs or Revenue officers.
Luxury goods were taken out of Thailand without being checked by the Revenue officers.
Tax invoices attached to the VAT Refund Application for Tourist were issued from a different store than mentioned on the form