What are the conditions for purchase?
Is the pre-investment based on certain conditions and terms to be signed by both the parties i.e., the vendor and the purchaser?
There is no reason to pay the entire sale consideration even before the starting of the construction. This is nothing but hidden plan behind such demand.
For purchase of property it is normal procedure to verify the parent deed/document, title document, encumbrance certificate, tax aid receipts, revenue records, field maps, lay out approval plan, plan of construction of flat, other aspects that are necessary for approval of lay out by the competent authorities namely, municipality, town and country planing department etc. The documents are to be properly scrutinised and vetted by an expertise advocate.
You may verify the items preparing a checklist and get a proper opinion by a lawyer in the local before venturing into the said investment.