17% would not be tax in Thailand. 7% is tax and 10% could be hotel service charge. You need to ask booking.com direct if these charges are included in what you are paying to the hotel.
If you read your confirmation it will state if you have to pay it or not.
It looks as though it is 7% VAT and 10% service charge.Edited: 25 July 2012, 11:02
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