Payments on account must be guaranteed
In new builds the buyer usually pays part of the price before receiving the home: reservation, deposit and stage payments during construction. The first additional provision of Law 38/1999 on Building Regulation requires anyone developing homes who wants to collect payments on account during construction to guarantee their refund, plus statutory interest, through a surety insurance policy or a joint bank guarantee, in case the works do not start or are not completed within the agreed period. Those payments must also be received through a credit institution, into a special account kept separate from the developer's other funds.
For the agency marketing the development, this boils down to a question to ask before signing the first reservation: is the guarantee in place, and which is the special account? Putting it in the document reassures the buyer and prevents problems later.