Am trying to get a value on and sell

I know that this is a 1859-O US . Seated Liberty Silver Dollar. What I dont know is km number. Or what I should consider a fair offer for it. Someone please help me figure this out

Hello and welcome to Numista!

It's KM#71. This is the Numista page for it: https://en.numista.com/catalogue/pieces11472.html
Here's the NGC price guide for it. https://www.ngccoin.com/price-guide/united-states/dollars/47/ I'd grade it as a VG. To really find out what is can be sold for you should check on ebay. Do a search for sold listings. Also, check the auction houses.

Looks like a counterfeit to me

It's suspect and we would need better photos to scrutinize for authenticity. It's also mounted in a bezel which would have to be removed for proper weighing and to check for possible related damage.

edge isn't right, silver plated brass replica.
photo of genuine coin for comparison

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For comparison.