When I upgraded the WiFi network for the holiday cottage I gained the ability to monitor the identity of the devices accessing the network. I can tell when a device attaches and leaves the network. I can also see how much data the device has loaded.
As the WiFi network for the cottage is a private password protected network, I'm able to work out when our guests are using the network. If necessary I can access journal records to detail exactly which device accesses the network at any given time.
I've noticed a correlation between bad guests, (i.e. they moan about issues without good cause) and the amount of use they make of the Wifi they use during their stay. Most people come for a holiday and are out of the cottage a lot of the time, these people complain the least and usually give us a good rating. People who stay inside the cottage most of the time have a tendency to moan, but people who do not use our WiFi network often moan about minor things.
It's early days yet, but it will be interesting to see how this theory stands up to the test of time.