'Virtually full tank' <-- If that needle was not on Full, they may have gotten you on the minutia. I over-fill the tank a little if I'm returning from any distance, to insure that gauge is well on full when I return my vehicles. This is due to being charged years ago for a full tank when the needle on the gauge had a little over the inside edge, I argued it and got it taken off, but learned my lesson.
Patrick