Too many to mention them all here but this is a golden oldie:
We had a real headache student at this one place I worked.
Nicest guy on the ground but thick as sh*t.
One of the owners of the place who was his primary instructor got so fed up with him that he told me to do the guy's dual nite XC.
I'd already been flying most of the day so I was pretty worn out.
The guy had preflighted this 150 already so I get in with him and ask about the fuel.
"Oh we got plenty almost full..:"
So we set off in this cr*ppy 150 with only one dodgy VOR at night, on our way to one of these "dark-hole" airports.
About halfway in the middle of nowhere I kinda notice both the fuel gauges waving at me from the zero-stop. So I point at them and question this guy.
He comes up with the following: .." it was so dark I could not really see any the fuel in the tank.."

So we make it to this airport straight-in and put in an equal amount as the book's usable...

That taught me to
always always always check the fuel myself.