How do you report income from an online selling service, if you did not make enough to meet the threshold for a 1099-K?

If you made a loss on personal items, this loss on personal items isn't deductible and isn't reported on your tax return.

If this is the case, you don't need to report the sales on your tax return. Just keep records of these sales in your tax records along with any proof that it was for the sale of personal items at a loss.

If you sold certain items at a profit, then you have to report these sales as an investment sale, even if you didn't receive a form 1099-K.

In TurboTax Online, you can enter the sale of your investment property by following these steps:

1. In TurboTax, open your tax return
2. Click on Federal in the left-hand column, then on Wages & Income
3. Locate the section Investment and Savings and click on the arrow on the right
4. Click Start next to Stocks, Cryptocurrency, Mutual Funds, Bonds, Other​​​​​​​
5. Choose Other then click Continue
6. On the next screen you have a dropdown menu where you can choose the type of investment you are selling

Please also read this TurboTax Help topic for more information.