Coin Cleaning ID?

As BadThad said, you have to learn. The only way to learn is to look at lots and lots of coins.

It's little things: If the color is 'off' (experience talking again) or uneven. If the field is too clean, the details dirty, but the pattern of the dirt is wrong.

Here is a start. With the next ten well circulated Lincoln cents that come into your hands (i.e. toss out the bright & shinny)... look at them under a glass. Notice where the grime and crud tends to build up and where it doesn't - for example the B & R in LIBERTY tends to catch more than the L or T, but the junctions of the L and T catch a little bit... Look at the field and notice the random scratches and dings from hitting other coins in a pocket. Contrast that to the hairlines in a cleaned coin that go in the same direction.

Now do the same with a handful of IHC that you know are/are not cleaned -- look in the headdress, the wreath, etc.

Also listen to your subconscious - if a coin somehow feels just wrong, it probably is.

Excellent information. Thanks Badthad and Bstrauss.