Many people select an air-conditioned house because of allergies, not just a desire for cooler temperatures, so opening windows may not be an option for them.  I think if you advertise AC, you really need to bite the bullet and absorb the cost this year.  Next year, take the increase in cost into account when you set your rates.   When I meet my guests, I ask them to not run the individual room units when no one is in the room (we have a mini-split heat pump system that can cool down a room in 5 minutes) and most seem to comply. Still, my electric bills are always very high in the summer -- it's a cost of doing buisness.  

I think your guests settng the thermostat to 62 is ridiculous.   Is there any way you can limit the temperature to 72 or so? 

We have two signs in our condo-one by the thermostat and one by the slider. Both signs state that if the A/C is set lower than 74 or the A/C is run when the slider or other windows are open, the A/C unit will freeze, resulting in total use of A/C for several hours. We have three ceiling fans in an 800 sq unit, so we think not setting the thermostat lower than 74 is a reasonable request. I also send this notice when I email the check in & condo use instructions. Although I can't be sure anybody pays attention to the request, I hope they do.

Maybe signs would help you.

Ok, I
worked as a HVAC Tech for many, many years. The first answer is to limit your
temps in the house, both summer and winter. I would recommend running nothing
but Honeywell Commercial Thermostats. They have many features others don’t
have, mostly ones to save electricity, like smart fan feature to occasionally
run the fan to circulate the air in the house, to keep all rooms an equal temp.
I would disable the program feature on the system to keep your house the same
temp day and night also. Remember, your walls, floor, furnishings all get to
the room temp, then radiate that temp back into the room if you re-adjust the
thermostat. If you keep changing the temp of the room back and forth you have
to also change the temp of objects in the whole house, plus the actual
structure of the house. That costs money. So in short, give the guest a low of
68 degrees, and a high of 74 degrees. That is considered a comfortable window
of temps for anyone. If not add or remove clothing.

Another option all homeowners is to contact
your local HVAC Company and look into adding something called an economizer.
It’s nothing but a duct going outside on the air intake side of the HVAC unit,
with a filter and and an electronic damper. For example in the summer if the
outside temp gets cooler then the inside temp, it will shut off the air
conditioning compressors, and just use the outside air. If after 30 minutes the
inside temp doesn’t start to swing downward, then the air conditioner will fire
up. The same goes for the winter time…. Just the opposite for heating. It’s
cheap and very effective.

Also if
your condenser is icing up in any temp above 65 degrees, you need to have
someone look at your HVAC unit. It may be low on charge, fan undersized, filter
plugged, too many registers closed or something else wrong. A properly
operating HVAC system will go down to the freeze point of the refrigerant, and
for R-22 (most systems out there), that’s about 63-65 degrees of indoor temp,
and the colder the outdoor temp the better for efficiency.

About
my history, I was a HVAC tech for 2 of the largest banks in the US, and a
property manager covering over 1000 branches each. So we spent millions of
dollars in testing to find the cheapest way to manage utility bills in our
buildings. The key to this was doing our own independent testing and having

unbiased results. With our HVAC adjustments, light bulb changes, and the use of
timers in our buildings we cut utility bills to 50% or less. And we maintained
this for over a 2 year period. In short, keep the temp in your unit consistent,
don’t use motion sensors, or timers. It
costs money to heat or cool all the objects in your house, and your house
structure.