Sgoss, those people you hear say "never clean any coin", are probably saying so with the mental image of the horror stories of persons who cleaned grandpa's gold coins with Ajax
The truth is, there's some coins we md'rs find, that they simply wouldn't catch numismatic interest, in the condition we find them in, in the ground. Here's a true story:
There was an east coast hunter, who after many years hunting, had a good # of large cents in his collection. One day he sat down and looked through all the dates, and looked them all up in the coin guide book. He discovered that he had a few that had supposed numismatic value. Better dates, etc... So he took them down to a coin store and asked what they would pay him for them. The guy at the counter looked at the coins, and gave them a pittance of an offer on a few. When the md'r objected that the coin-book was giving them higher values and grades, the coin store guy: "
they're too dirty and corroded". When the md'r heard this, he asked: "
Oh, then if I clean them up, THEN would you make an offer on them?". The coin-store guy BRISTLED at the mere word of "cleaning" and warned him: "
if you clean them, then for SURE no collector would ever want them! Don't ever clean coins", blah blah blah.
With that, the dejected md'r took his coins back home. He figured that as long as they weren't worth much, he had nothing to loose by at least trying to make them look better. If for no other reason, than just for home display trays. So he set about studying all the different ways to clean copper coins. He experimented on a few common ones and IH's. He found a least intrusive, least tell-tale, yet effective way, to leave no abrasion, no un-natural color, etc... I forget which method he decided on.
About a year later, after the long process of whatever method he'd chosen, his coins looked much better, yet without any apparent trace of his effort. He took the same coins back to the same store. The same clerk waited on him again. By this time, more than a year later, the clerk apparently forgot about these coins, and this guy. So the md'r did not say anyting either, or remind him, nor did he say anything about that they'd been cleaned.
THIS time, the coin-store guy got real interested, and started offering higher prices right off the bat!
So the moral of the story is: The old addage of "never clean your coins" is not always correct. It's a matter of HOW you do it, and whether it's the lesser of two evils in some cases.
I'll try...