Well in that case you need to find someone locally to help out. Have someone look after the keys for you – someone you can trust and not necessarily an agent – it has been known for agents to rent your property out and pocket the money – not all agents would do this but why risk it.
It has already been mentioned that agents in this partiular case are not performing the function hence the reason for the question.
So unless you would be willing to come and show people round yourself or you know someone locally you can trust you will need to find some other method of performing this function. Who do YOU trust with your keys and property?