Landlord wants me to pay utilities in advance?

Hi, currently accepted to rent a house in Haarlem, and I have some concerns about the rental contract.

The landlord has requested that all utilities remain in his name, and that we pay for utilities in advance using an average for a 3 person family (a figure he says will be provided to him by the electricity/gas supplier). At first I thought the idea was absurd, but after my research I learned this is a practice in NL.

My concern is that we will be paying too much. We are generally pretty conscientious when it comes to energy/water consumption, and there will be periods when one or all of us aren't at home (work trips, summer holidays, etc) that will dramatically reduce our usage.

Will the actual usage be compared to the amount paid, and will a refund be provided if we have overpaid? I've  asked our property manager but she is being vague (or perhaps it's a lapse in communication) so if anyone could shed light on what is common practice in this situation it would be appreciated.