Whose door it is
No door is opened on somebody’s word. Before anything starts you are asked for proof that you live there or are entitled to be inside: ID with the address, a rental contract, a booking confirmation, or the owner or the agency confirming it by phone.
That rule is the same for holiday guests. With more than 5,000 registered holiday lets in Dénia, a lot of openings are for people staying in someone else’s property, and the host or manager authorises them: see work for holiday-let hosts.