Kiosk prints often too dark. Why?

I wouldn't be so concerned about this if it wasn't that 1) I think I know what I'm doing when taking pictures(with DSLR et.), and 2) Many others seem to produce better images(brightness/darkness-wise) with the simplest of cameras without a clue as to what they are really doing. I have an advantage in that I work P/T in a 1-hour lab and can fix my pictures to look just fine. But why should I have to?

My images look great on the camera's LCD and on my computer monitor. Little need for any corrections when viewed there. The EXIF data always looks reasonable, too.

I do understand that often times the Kiosks (Fuji mostly) will "auto enhance" the images. I have control to turn this on or off. Seems as though the dark images often lighten and the opposite. Also seems common for my darker images(contrary to what I just said) to get darker. Severly cloudy days seem to approach early evening even when steps are taken to use higher ISOs or wider apertures. And just as often the same things occur in "P" mode. This happens with all of my (3) cameras. Canon XS, Panasonic FZ30 and Canon A610. I would quickly blame the Kiiosks if not for the fact that other folks' pics often come out just fine.
Any ideas?