In your ShopAssist cart, you are required to factor in any domestic shipping costs that may apply to their order (for example: ColourPop orders under $30 have an additional $4.99 for shipping; Bath & Body Works charges $5.99 for shipping for orders over $10).
If you do not add this fee in before completing the payment for your ShopAssist order, you'll be notified that an extra charge needs to be placed to complete their order.
Some extra charges may occur if you submit your ShopAssist order during a specific sale, but the sale price has ended by the time your product is ordered – you'll have to make up the difference with a secondary charge as well. The reverse also applies! If you submit the order with the regular price but then a sale starts then a credit will be applied to your GoSend account.