Which of the following statements is incorrect?

a) Sales tax collected by a seller is recorded as an increase to sales tax payable.

b) Freight in is used in the calculation of net purchases.

c) A purchase discount is calculated after subtracting returns and allowances from gross purchases.

d) If an item is shipped FOB destination, the seller is responsible for the shipping costs.

e) If a seller makes a sale under the terms 2/10, net 30, the sales discount is only available if the buyer pays within the 30 day window.