something fairly old
At the end of the day your find is just that, your find. You're free to do with it as you wish including both as much to preserve it as possible or to completely destroy it.
Lets use the 1916-D Mercury Dime as an example.
First scenario. You dig one, wrap the dirt caked coined in a paper towel, place it in a carrying case, soak it in water, then gently rinse. What you find is an example in VF condition that shows little evidence of being dug and you sell it for $3,500 on ebay.
Second scenario. You dig one, excited by the silver edge you rub the dirt off between your fingers causing countless surface scratches, then you take it home wash it off and polish it so its nice bright and shiny. You put the coin on ebay and it brings $1,000.
I usually suggest that folks take care when handling their finds not in an attempt to be judgmental of them, but rather to help them retain the most value of their find and some just don't know. Some still want a flashy piece, and thats okay as it is theirs.
