The IRS says to include your Form 1099-K on your tax return. Add a negative entry for the same amount to show you didn't make a profit. TurboTax will do this automatically if you're reporting an overall loss. If you have gains and losses on the same Form 1099-K, don't enter more than Box 1a as your cost.
Losses from the sale of personal–use property, such as your home or car, aren't deductible.
The cost of a gift sold at a loss is the fair market value of the item at the time you received it.