I've been searching around and cant seem to find a clear answer to this... I'm a rookie collector, which I guess is obvious from the fact that I'm even asking this question. I've cleaned coins. Nothing of value, just things that I like and wanted to get looking a bit better. And when I've done it, I've used simple, seemingly safe methods. Pencil erasers, ketchup, etc. I've read the various threads on cleaning, that you should never do it, dealers can spot a cleaned coin easily, and of course it can decrease the value of the coin. But what I don't understand is why, exactly, a cleaned coin is perceived as being less valuable and somehow damaged? If you're using a cleaning method that can't do any damage to a coin, what's the real harm? Take the pencil eraser trick. I don't think some light rubbing with a rubber eraser can put any kind of a defect into a metal coin. Maybe if you accidentally had some sort of abrasive or foreign object stuck on the eraser and dragged it across the surface of the coin, sure, that's bad. But I don't see how this can detract from a coin's value. It's essentially removing years of dirt and grime, especially when we're talking about stuff from circulation. Shouldn't the value of the coin be in the metal, the original product that was minted all those years ago and not in the grit that was picked up as the coin travelled from person to person? Also, could cleaning reveal something about a coin that might be obscured by dirt and grime? Seems better to me to clean a coin and really get a good look at it's surface than to try and ascertain the condition of it through years of junk.