About the only way is to check Ebay used listings or Craigs List. There is no true resale market - it's informally done at those sites or if your a Club Member here you can sell a panel on that marketplace section but never in these threads.
I've sold two TV's here in the past but never within open threads - only where Members paying Club dues to AVS are permitted to Sell items. Much depends on age and warranty coverage but I would not set your expectations very high especially if you lack an extended warranty that is transferable.
Often it's simply better to transfer use to another room or someone in your family since you could still get a number of years out of the panel and the cash gain would be minimal in a sale on a panel that old considering where the prices have dropped and technology gained in those three years as there are so many budget panels today on the market - the price 3 yrs ago was MUCH