In the usual circumstances, when there is a sale of your item, we will pay you the selling price less the agreed commission.
Hence, when we deduct from your monthly payout the amount of the items we returned, we will only deduct the portion that we pay you in the usual circumstances.
This means that we apply the commission to this item, just to avoid charging your more.
Here a simplified example to explain further the concept:
If a customer purchases an item for SGD 100 and you have a 35% commission, the amount paid to you would be SGD 65.
In case we need to return to you this items, and shall we not apply the commission again, we would write off SGD 100 removing from your payout an amount which is higher than what initially transferred to you.