Cleaned Coins

Hairline scratches are a big give away for harshly cleaned coins. Things that are too bright have usually been over dipped. Check and make sure the luster matches the wear. Things with wear shouldnt be the same color they were when they came off the press.

I think the best way to describe it is youre looking for inconsistencies. Something to shiny for the wear level, or scratches that shouldnt be there, an unnaturally bright color and so on.

ebay can be a great learning tool for it too. Look at a ton of pictures of graded coins that arent details then look at a bunch of the details cleaned ones. The more coins you see the more the inconsistencies will stand out.

"Cleaning" encompasses a huge gamut of possibilities, with an equally-huge range of possible appearance. I realize this is pretty general advice, but it applies to just about any aspect of evaluating a coin: The best way to tell a cleaned coin is to know what an uncleaned coin looks like.

Specialize. Knowledge is the imperative in numismatics, and far easier to take it in small bites even if your intent is to cover multiple issues in your collecting. Each different type has its' unique reactions to outside interference, differing grading standards. Don't try to learn them all at once. Pick an issue, and get it down pat. With that in hand, you'll be rather surprised at how many generalities carry over to the next, but if you try to do too much at once you'll only find confusing and conflicting "rules." This is probably part of your difficulty with detecting cleaning after collecting for a while - you're trying to learn too much at once.

I would just add that detection of those telltale hairline scratches often requires excellent lighting.

with silver coins:
Beware of coins with wear, that are clean. If the coin was circulated enough to show wear there
will be some soiling between the devices and the fields.
AU and Unc. coins should show luster in protected areas (or more) unless they are very old.
Very old (seated era) coins will be toned and the toning is actually how original surfaces are determined.

Look at the dull lifeless appearance of known cleaned silver to gain expertise in recognition.

If a coin has been dipped in a cleaning solution, there will be no scratches, no rub marks, basically nothing from harsh cleaning. However, one of the best things I look for is on older coins where the inside of letters and numbers are free of dirt. For example the inside of a B or P. The smaller the opening, the less likely if no dirt, has been dipped in a solution to clean the entire coin. And it's not just letters and numbers. For example the wheat lines on the reverse of a Lincoln Cent. IF an older coin, should be dirt inside those lines too..

I've always wondered why if most collectors or dealers are not big fans of cleaning coins, why the industry produces so much coin cleaning supplies. Somebody is buying that stuff and using it, and folks are buying the cleaned coins to support that side of the business. Just thinking out loud...