Chuck
Most flying schools instructing on the Cessna 150 where I have seen them fill the tanks and then seen two 200 ib plus guys jump in are overweight and it happens all the time.
It seems it is the same here in Canada.
However when I owned a school I made sure my instructors paid attention to the rules and regulations by having them sign an agreement that if I employed them and found they had intentionally or stupidly ignored the rules and regulations I would terminate them.
I had three Cessna 150's one Tomahawk, two Cessna 172's, one Grumman Cheetah, one Piper Geronimo and one Robinson R22 Mariner so there was no excuse for flying a Cessna 150 overweight.
The way I look at it is if they were willing to break the rules over something so easy to avoid as flying overloaded they were not employable.