Took an EANx course the other day. The book and instructor made a point of saying that you should not get an enriched fill if the filler cannot provide certification and an annually-issued verification of the quality/accuracy of the fill (without my handbook in front of me, I forget exactly what these were but you get the idea). For those who use Nitrox, do you actually ask for such verification before getting a fill? I would see doing it if the place looks suspect or maybe if it's in a 3rd world kind of location and you have some doubts about the place, but I am wondering if you are getting a fill from an average shop in the US if people really ask for these certificates or licenses.