<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by Sweet Willie:
she made the comment while we plucked our bags off of the luggage carousel that her pieces of luggage were quite dirty and needed cleaning. </font>
I've noticed that handlers will place wheeled bags on the belt with the wheels toward the upper side; presumably this helps prevent the bags rolling around on the belt and getting jammed.
The problem comes with bags that aren't basic black; usually the most colorful side (the back side when the luggage is being wheeled) is the side that is in contact with the belt when it's set down this way. I have a red & black Swiss Army bag; the red side gets dirty from traveling on the belt.