So they feel they need to hide them in the dark until closing to get any deal done.

@Micah Hensley, I'm just shooting in the dark here but it sounds like you're prioritizing drive time and convenience over the investment perhaps?  

I was thinking of buying or painting the front door a  dark navy blue.

 - In other words they are lying and don't want you to send someone over to see that they are lying, and that they snuck a dog in there, and that they have been smoking in your place etc.  

Newly finished space will likely need a hard wired smoke detector.

My miter saw blade was smoking when cutting it @Marcus Auerbach

I honestly don't care if they smoke or not, but I know some smokers WILL smoke in the house/apt and because of that risk, they get a ding. 

You do not want to show a dark house, or let the refer remain closed with the power off, and water is important...possibly  for irrigation, and certainly for potential need of the restroom.

The plumber recommended a "smoke test."

After a guest mentioned that they had trouble finding us when they arrived after dark, I added a new house number at the end of the house closest to the driveway, which is lit by the street light.