Most people can see the telltale signs of cleaning when they see lines all over a coin but most can’t tell when the cleaning isn’t harsh. Over the years some coin “doctors” who have learned to perfect their cleaning methods and sometimes this is barely perceptible.
Whizzing is one example and a person good at whizzing will cleaned the coin with a fine grit “tool” that creates lines on the coins surface. They then use an acid to remove the higher points of the metal they “moved” with the tool.
The ridges and valleys of these “cleaning” lines are extremely shallow and small and hydrocloric acid can be used to help make them less noticeable. I am sure there’s other methods but this will remove the natural struck layer of the coin that is molecules thin.
A “professionally” whizzed coin fools most collectors so it’s important to turn the coin in the light and in all directions to see the barely perceptible cleaning lines.
Also cleaned coins don’t have to be cleaned on both sides, some might just be cleaned in a small area; maybe it was someone’s attempt at cleaning and they stopped short when they say the lines. Either way the grading services will be labeled cleaned 99% of the of the time and sometimes one company will details grade a coin cleaned, then the other grade it problem free.
The author had a 1928 Peace Dollar graded AU58 by PCGS and I carefully cracked the coin out and resubmitted. The coin then came back UNC details Scraped. I saw the scrapes but it didn’t details the coin before. So cleaned coin results can be mixed but not way a coin goes from circulated to not circulated based on marks on a coin.
Here’s a video on graded cleaned coins to help you understand what cleaned coins look like. I purposely sent these coins of as an educational tool.
Related Guide: Detecting More Cleaned Coins