What do you do if a guest wants to charge their car at the property?

Set up the charging point as a separate item with its own metering and its own QR code, separate from the accommodation, so that you can set your own price per kWh which may be higher than the rate inside. A guest already staying in the accommodation pays from the same credit, separately specified in their overview; a passerby can pay and charge without a booking or pass, using only an email address and code. If there is no charging point present, this does not solve the problem for a guest who simply wants to run a cable to a power outlet.