The gunk buildup (and the unnatural color) on the S are dead giveaways. Look around the wreath on the reverse & the legends on the reverse/obverse.
Coin cleaning wasn't taboo like it is now, 40+ years ago, in fact, many people cleaned their coin collections regularly because shiny was valued more than original as far as surfaces go...
The more you see, the better you get at picking them out. After handling a couple thousand, or ten times that many,
Morgan dollars, you get to a point where you can start cherrypicking the original from the cleaned & the better from the average or below average.
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