If you choose to fulfill orders yourself, Amazon will charge customers standard shipping rates for media products (books, music, video, DVD, software, and video games) sold by Professional Sellers, and to all products sold by Individual Sellers.
The rates are determined based on the product category and shipping speed chosen by the buyer, and then deposited through the Amazon payments service to reimburse you for shipping costs.
Unfortunately, this means if your shipping costs don’t match the platform rate, you lose the difference in any additional shipping costs you incurred.