Have you ever seen posters that ask you to pick out all of the safety hazards. They are usually funny to look at and interesting to pick out all of the unsafe hazards.

This photo kind of reminds me of them. You can see multiple no-no's for fueling a jet.

Tie wraps on connections
no safety wire
Threaded bolt as a stopper.
Festo on the suction side
You can even add items like ensuring all connections are in good condition. I have seen where someone has used a knife to cut off an old fuel line leaving a score line in the barbed connector. The score line works like a channel for a leak to occur.

Marc's comments above are right on the money!! Good points for doing a proper fuel system install.