Remote locks, thermostats and definitely be willing to have and spend the time to answer calls, texts and emails from your guests.

Bluetooth thermostat that hooks up to your phone to control temperature.

Remove the "complicated drain" and let them use a rubber stopper, no programable thermostats, no fancy ceiling fans with remotes/wifi, no fridges with water/icemakers, etc.

Once the filter was replaced and we hired a handyman to teach the tenant how to use the thermostat all problems were resolved.

@Blair Poelman, how do I go about putting them on a thermostat?

They have subliminally an internal set financial thermostat in their mind and recede once they hit it .

If you can't self manage (which everyone thinks is easy - but it's a LOT of work so depends on your available time to devote to answering basic questions over and over, calling 3 cleaners to replace the one that called out for the 5th time in season, calling an A/C company because your guest turned the thermostat down to 65 in 100 degree weather, etc.) then either go with iTrip if they have a strong franchise in your market or a mid-size local company with a good reputation.

If I tried to be a Realtor, was showing a home, and someone told me the kitchen didn't "feel warm," then I'd turn up the thermostat, declare the problem solved, and tell them to write an offer or GTFO. :) That sort of approach works for mortgages where it's a number you can quantify and exactly measure, but not for being a Realtor where it's an aesthetic and a feeling. 

Hi BP,I am planning to lease out a separate room in the house with its private entrance, kitchenette, bathroom and separate thermostat.

And put a lock on the thermostat for heat/cooling, because that will be another problem area.