If you sell a property in Thailand then you will be taxed as follows:

1. A with holding tax ( from 0 to 37%) the tax rate varies based on the income of the seller. The basis of the tax is the government appraised value less a deduction of between 50% and 92%, depending on how long you own the condo. The longer you own the condo, the lower the deduction from the appraised value, and therefore your with holding tax liability is higher.
Income of 0 to 80,000 Baht: 0%
80,001 to 100,000: 5%
100,001 to 500,000: 10%
500,001 to 1,000,000: 20%
1,000,001 to 4,000,000: 30%
4,000,001 and above: 37%
Specific withholding rates are as follows:

92% if you have held the property for one year;
84% for two years;
77% for three years;
71% for four years;
65% for five years;
60% for six years;
55% for seven years;
50% for eight years or more.

2. Business tax of 3.3%. The sale price or purchase price is taxed 3.3% depending on which has the higher value. The tax is paid in case a buyer has a property in their possesion for less than 5 years.

3. A transfer of ownership fee of 2% of the appraised price.

4. There is also a Stamp Duty of 0.5% of the appraised price. This is only paid when a specific business tax is not applicable.