The vendor has the right to receive the full amount of the agreed price from the purchaser at the time the sale contract is settled.
Frequently the vendor has already received an advance payment on that price, generally as a deposit: in that case he will have the right to receive the difference to make up the full agreed price.
The vendor has the option to allow the purchaser a deferral of payment, with or without interest.
It is up to the discretion of the vendor (based on the trust he has in the other party) to demand and obtain from the purchaser guarantees as to the deferred payment of the price.
These are the alternatives: a simple mention in the contract of the deferral of payment; issuing of a bill with or without mortgage backing; registration of a legal mortgage; conditional ownership until final payment has been made.
Given the complexity of the subject and especially the need to assess each single case on its merits, the best advice is to consult a notary who will be able to suggest the best solution for protecting your rights.
Lastly, a word about means of payment: given that the law forbids the use of cash for amounts over Euro 12,500, the alternatives are basically a non-transferable bank cheque (i.e. a cheque drawn by the bank which guarantees it is covered), non-transferable personal or postal cheques (lacking the above guarantee) or a direct bank transfer.
Of these means of payment, the one most used is certainly the bank cheque because, since it is guaranteed by the bank, it is safer for the vendor: the vendor may therefore insist that the sale price be paid in this manner since it is now the established legal practice.
It not infrequently happens, however, that the bank, which is financing the cost of purchase and which has been approached by the purchaser about a mortgage, does not immediately make the funds available to the purchaser, but makes their availability subject to the fulfilment of all fiscal and registration requirements the notary must carry out and in some cases even the expiry of a legal term: to this end, the purchaser gives the bank an irrevocable mandate to transfer the agreed amount directly to the vendor, so that the lending/mandated bank, once the notary acting in the case advises that all formalities relating to and consequent upon the conveyance have been correctly completed, will pay the agreed sum directly to the vendor.
This practice on the one hand assures the bank that the customer it is financing gains full title to the property and on the other hand provides a guarantee to the vendor since the purchaser/borrower, having once given such a mandate, cannot revoke it and prevent the bank from paying.