Had a lady at a garage sale do the same thing with old sci-fi paperbacks.

Ran the same math last year and it hurt. Most guys never check because they are scared of the answer. Charge for the finish and the panel work or you are just paying yourself to be busy.

Funny thing is I once spent half a day hunting a leak in a strip mall and it turned out to be a condensation line from an AC unit dripping into a bucket some tenant left behind a wall. The musty smell thing gets me every time. I have walked into spots where the smell was so bad you could taste it and the guy with the keys says oh that's been like that for years. A $40 moisture meter and five minutes poking around would have saved your property owner a few grand. Then again I am the guy who ignored a drip in his own basement for a whole winter, so who am I to judge.