Real silver will be marked, like SirS said, you are looking for a mark that says sterling, 925, ster., or something to that effect. Some older pieces that were made from coins will say coin or 800. Now if you have European pieces you have to look for the hallmarks, little characters that when translated will tell you the maker, city it was made in and the year.
Things that are NOT silver are sometimes marked, A1, IS, nickel silver, german silver, anything that says silver.
My favorite site for looking up hallmarks is
Online Encyclopedia of Silver Marks, Hallmarks & Makers' Marks .
As far as a place to take and sell, I would go to an antique store, they would come closer to paying you a fair price for it, so they can resell it.
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