Re: Dinner charge
I used to get a lot of that in a previous job, supporting Very Smart People (not sarcasm!).
Often they'd make a change to their models, get an error, think it through, check seven or eight things, then call me up to say something is broken after a few hours of attempting to fix it themselves. When asked, they'd often tell me that nothing had been changed, because by the time they called me they'd already been trying to fix it themselves for a few hours and had lost track.
I got a lot of mileage out of file/folder comparison tools. "Someone changed *this* CSV and I'm pretty sure it didn't used to be tab-delimited".