Posters have been advocating the practice of watching the line service
person fuel the airplane.

I take this a step further. If not at a self-service facility (which
always saves $$$), I request the line person to bring the truck around and
then I fuel the airplane. I sniff the first fuel out of the hose and rub a
few drops between my fingers and thumb (jet fuel smells different and feels
different). I then add the amount I want, and I am able to avoid damage to
the bladder and to the float mechanism that sends info to the fuel quantity
guage.

Yeah, the FBO people sometimes think I'm weird, but in the end, anything
and everything on the subsequent flight is my responsibility, both legally
and morally, and I'm not going to bypass a simple step like direct control
of something that could ruin my whole day. Been doing it that way for over
forty years, and I'll continue, until the day I stop flying.