All taxes are to be paid locally according to the local law. Transfer tax rate for the estate transactions (Stamp Duty Land Tax) is 4% . That is calculated on the base of your declared price.
What price shall you declare then? The cadastro office will ask you for the official govermental value document, which manucipality gives, and which usually is ca. 40-60% lower than the actual market value, plus the experts report (official valuation) which will cost you around. 1000 TRY.
The experts report is for showing the market value, what again in practice as I see since 4th of March 2019 is not (…) the exact market value. Anyhow the same rule works – you can not declare less then the govermental documents says. But also you are not forced to declare what the experts report says, as the owner of the property you are the only one who can decide for how much you are selling.
Nobody can forbid you to sell cheaper than expertise says, if this is what you want/need to do… The Buyer shall pay taxes half-half with the Seller, but in practice the Buyer covers this cost.