There was a small installation charge of $100/unit.

If the GC charged you for that time, add the cost in the log too.No need to go crazy with phone snapshots, but keep emails or texts as backup just in case.

There are lots of application websites that charge the tenant but not the owner.

. ;-)  your right because I dont charge to consult for sub too.. 

But I wasn't trying to charge to teach others a system. 

I have had legitimate folks ask to see my place in person for a 5 week rental and I did a FaceTime tour with another that was out of town.  

They charge a premium but are allowing them. 

If they're looking for $10,000 seed money and you have $10,000,000 sitting around - plus the due diligence checks out (legitimate opportunity) - that's relatively low risk for a good upshot.If they're looking for $50,000 seed money and you have $75,000 liquid, absolutely not.Personal financial position, coupled with due diligence, are important.

And do not charge or have minimal charges to provide this feature? 

You need to know what their minimum trip charge is and hourly rate.