BPF
At the school I occasionally teach at any instructor that deliberately flew a lesson with the aircraft over its certified max gross weight, would be immediately fired.
I heartily agree. We usually ran with 15 - 17 gallons - never any more. The one time I asked if we should fill up (this was at 14gal), it was denied. By
foxmoth's link's reckoning, this should have been in limits.
It didn't seem relevant to ask the instructor what he weighed exactly, so it was taken on trust that W & B were in order - given that both our lives were in his hands. Luckily, he was a fine and patient instructor, but he must have felt similarly cramped in the little 152. There wasn't much swing room to hit me over the head with the fire extinguisher when I did something stupid. Which was frequently.