First of all, the television is heavy and bulky, so it's going to be hard to mail it off to a third-party seller, and the shipping costs might be too high. The smartest option would be to sell it to the buyer directly. Secondly, there's a lot of information on selling gadgets, but not specifically TVs, which require a different approach. And lastly, it's hard to put a number on it because of the big discrepancy between prices in the used-TV market.
Where to Sell
Although people sell their TVs on sites such as Amazon and eBay, the best place to unload them is Craigslist. After all, you can arrange for buyers to come pick it up themselves, so you don't have to mail it off. Since it's also a potentially bigger financial transaction, you might prefer to ask for the payments in cash, which is possible with Craigslist.
Cut to the chase: Sell it on Craigslist.