someone bought a condo for 2.4 m 2 years ago and is going to dispose it at 3.3 m;

she will be responsible for the transfer fees which is 2% based on the sale price; paying 3% commission to the agent; another 3% in taxes on the difference between the purchase and sale price; and in addition will also have to pay personal income tax;

can she deduct the transfer fees and commission when paying tax ?

what's the net amount she can expect after completion of the above transaction ?

She should net around 3 M baht depending on appraised value land office has for property.

Fees you mention cannot be deducted when paying withholding tax at land office.

Once the transaction has been completed an individual seller will have the choice either to consider the withholding tax he/she has paid at the land department as his/her final tax payment on the condominium sale or to integrate the income resulting from the sale in its personal income tax and apply the withholding tax credit against its tax.

Unless she was cash short and needed to sell why did she agree to pay all the transfer cost? She should have tried for 50/50 split of transfer cost or buyer pays transfer fee but not seller pays all transfer cost.

You/your lawyer need to negotiate this before you sign contracts.

The seller should not be paying all the charges

From OP it looks like the negotiations are already done and agreed.

I know in Thailand these are sometimes split. As buyer i have had no objections to split or sometimes pay the transfer fees in full if the price is right but i have always refused to pay the sellers taxes on his capital gains.

Everything is negotiable, even the agent fees.