1. You can get the said information in writing from the builder since from the details of the payment the 1st buyer made so far, it will be clear whether any such payment has been made by a Bank or not.
2. Moreover, in case of such mortgage before registration, the lending banks take consent from the builder and sometimes execute a tripartite agreement with an undertaking that the builder has no objection for the buyer's creating mortgage on the said flat and also that the said flat will not be sold by the builder to any other person.
3. Your should insist for a written confirmation from the builder that no mortgage has been created upon the said flat by the 1st buyer.
4. Same affidavit shall have to be taken from the 1st buyer also.
5. However, by taking a glance on the payment detail;s of the 1st buyer, you shall understand whether any bank loan has been taken by him or not and if bank loan has been taken then certainly the said flat has been mortgaged by depositing the originals of the allotment letter and the agreement for sale.
6. Take extreme care in this regard in your own interest.