The sale agreements and transfer of the owner shall be only done in the deed(tapu).
However, making the contract by Notary Public doesn’t always secure the investor because an annotation (Şerh) must be put showing the pre-contract is made.
Using this way only may not even be enough to secure the investor. Therefore, as mentioned below, the deed records must be checked.
There is only one exception to the validity of the contract.
If the buyer is a consumer who wants to buy a single house for own use, the seller can not claim that the contract is void. With that contract, the buyer can claim the ownership, if the seller is still holding the ownership.