Risks of buying a builder flat from first onwer without registry

Dear Sir, I am willing to buy a builder flat from the first owner in Gurgaon. The possession of the flat is still pending as it is under construction and registration in Haryana Govt records is also due. I do foresee number of risks in this case and need your suggestion if these risks are right and what is the right and risk free mechanism, if any, to move forward. 1) Firstly, since it is not registered, there is no way to validate builder records for ownership of first buyer. 2) Even if agreement to sell is done and seller back tracks after 10 or 20% payment, it will be a big hassle as no legal authority is involved to verify flat ownership and builder records. 3) How to make sure that the seller and builder are not selling anyone else's property? 4) Even after all payments, we later come to know that builder has not entered it in our name as there is no record of this in govt records. This could be a nexus between seller and builder. 5) Are there any charges for transfer of ownership change in builder records? If yes, who pays for it, Seller or Buyer? 6) Do you suggest that such transactions should be avoided till the property gets registered? Awaiting your response. Thanks & Regards, Vivek Gupta