Since the gun is not a collector's piece, and since you have no personal knowledge of what may or may not have happened to it, I would just sell it as-is and not be too concerned. It is great to be upfront on this type of thing but without knowing the details, all you can provide a potential buyer is speculation.

It is not uncommon so see some difference in color of blueing between parts on guns as the get some age, and reasonable buyers of shooter-grade revolvers usually aren't too concerned about that, unless it is just plain unsightly.