I would suggest getting a lock on the door that is programmable so that the guests can come and go as they please.

The air heat was blowing through the vent at 66 degrees and the thermostat was set at 74.

The unit is now trashed (expected) but things are missing (e.g. bathroom mirror, thermostat). 

I do have regulated locked thermostats so I know there is no- over use  

I'd give more consideration to the end user interface... the devices, how well the rooms heat up, air flow, and thermostat controls.

I also would take a course or two that will give you some computer skills, you don't have to be a programmer, but having the ability to do the easy stuff yourself is a good idea. 

He may think the heat is on because he adjusted the thermostat before he left.Give him notice that the heater is not kicking on and you intend to enter the unit to inspect and verify the heat is operating.

We've now started investing in a few high tech features such as programmable thermostats and smart locks to keep up with the demands of our target audience.

Think clunky looking light switch & electric outlet covers, thermostats, door knobs with "brass" plating peeling off, etc.

On the money saving note I wish I could post photos so you could see my 12$ smart watch, my air mattress ,and my scotch taped at 68° thermostats.