It depends -
You will need to include the full amount reported in Box 2 as gross sales amount. If this extra seller credit amount was already subtracted from the box 2 amount, then you will include the reduced amount as gross income. If this seller credit is listed on the 1099-S but not in box 2, then you will include this as a selling expense. You would be able to enter this selling expense on the same page as your sales proceeds (See screenshot).
