Identifying Cleaned Coins

Not on those Mercury dimes the little lines that would indicate a brush or wire wheel of just something slightly abrasive. However, I don't think those were dipped in something like a jewlery cleaner since there is still evidence of dirt inside the letters and numbering.
For example on the 26S around the date, lots of what appears as dirt. However, such things can be addded with exposures to just plain old dirt and a bit of water. A touch of gun bluing solution or even just laying around on a window sill.
A cleaned coin, if done carefully, is not an easy thing to tell by the average person.