Personally I wouldn’t be playing Johnny detective hanging out in the area waiting to sniff out the culprit .

Fall & Spring HVAC Service Target Date: April and October This service can aid in early detection of costly problems and save the cost of expensive, emergency service.A/C Service Includes: Check condenser coil, adjust operating pressures, monitor safety controls and starter capabilities, clean or replace filter, adjust blower components, calibrate thermostat, measure for proper temperature differences, clean condensate drain, tighten electrical connections, measure voltage and amperage on motors, lubricate moving parts.

The best thing to do is hire a private detective.

How can I detect a roach problem during the daytime at the actual check-out appointment? 

The letter needs to say "Bob needs to have a dog that is capable of detecting a negative emotional response to certain stimuli and can help distract and redirect Bob's attention from that response and guide him towards blah, blah blah....

According to 399-ccc: “It shall be unlawful for any person or entity to distribute, sell, offer for sale, or import any solely battery operated smoke detecting alarm device powered by a replaceable, removable battery not capable of powering such device for a minimum of ten years.”

You shouldn't spend all your time playing detective on behalf of others.

Sit down with them awhile and do some detective work, too, like actually call insurers, trash and utilities, mortgage brokers, tax authority, etc...Your calculations will only be as good as the raw numbers (and I find sellers may give rosy estimations sometimes, rounding income up and expenses down)...

The American Leak Detection company came out to check water coming into the house, and no leak was found.

This is common and can sometimes be very difficult to detect, even for seasoned pro's.