A card is only actually worth what someone is willing to pay you for it.
If your LGS doesn't want it, your only options are to sell directly to someone, or to sell online.
I have bought and sold on ebay. Recently, there are a lot more counterfeit cards on ebay. But the risk is with buying. When you're selling a legitimate card, there is no problem. For high value cards (>$250) ebay does now require that your cards get shipped to their authentification service first. Then they ship to the buyer. This could be easier for you. Ebay will take a percentage of the sale as a fee. This can be a good option if you ultimately want cash in your bank account.
I have also sold cards to TCGplayer.com as a trade-in. They are currently buying Kaladesh Masterpiece
Mana Crypt for about $650. There won't be any fees taken out; you will get that entire amount. This can be a good option if you want money (store credit) to buy more Magic cards.