Yes, they should be clearly identified.
I'm not aware of how well they would sell. Most sentiment that I know of is against polishing except for one's personal collection, and even then many times people are against polishing. Most of the positive feedback about polishing that I've been aware of in the past has been because there was one much-loved man who was doing polishing and people wouldn't want to hurt his feelings. That was Leroy.
But Leroy has passed away, and that brings up the question of who might still be available to polish? And would they be anywhere near as affordable as Leroy was?
So that's one other thing to consider -- if you were polishing marbles in order to sell them, would the cost of polishing be more than the marble could bring at market?
As you can see, I have more questions than answers. But I think I've given a pretty good summary of issues involved, if not resolutions of the issues.