John100 I never bothered to ask the dealer. I do a decent amount of dealing with used items and reselling and one thing I learned very early on is that anyone who wants what you have in order to turn a profit will never pay you what someone who wants the item to own/use will. Maybe I'm wrong with coins (not something I'm well versed in)?
As far as cleaning, something I learned the hard way long ago. Once upon a time I was a teenager living alone with a need for money so I decided to cash in the coin collection my grandmother had given me -- mostly Morgan and
Peace dollars. They were kind of dirty so I went out of my way to take some silver polish to them before taking them to the local coin shop. I still have nightmares about that.