the 50c has been ruined, i love the coins of newfoundland and have tried to get as many as possible over the years, thankfully i have a 50c from edward VII but the one in your picture looks shocking compared to it.
to be fair if some one has a coin in his/her collection that they are not happy with because it looks dirty and they have no interst in selling it on then they can do what they want to it imo. i personally wouldnt clean unless it was dug or in really really bad shape but if it still has a place in your collection after they its your own personal decision
don't know calum my personal collection isn't cleaned as such perhaps a dip in acetone to remove crap but that's all. i do admit to owning about 3 cleaned coins as they are the only examples i have of that coin but my general rule is never clean.