If your Gross Proceeds on the 1099-S has already reduced the sales expenses, you can then enter the same amount under the Net Proceeds. In most cases the amount Gross Proceeds amount has already been reduced by any fees or commissions.
However, if you need to report fees, commissions, or other sales expenses that were not subtracted from the proceeds reported on Form 1099-B, you can enter these expenses under the blue link sales expenses, below the Net Proceeds on the screen. Please see attached image.
