The CREDIT or DEBIT to Buyer or Seller will be determined by agreement in the purchase contract or other documents.
Line 1400 is a total line. It takes all the charges for the page, from item 700 through the 1300 series and totals them for both Buyer and Seller.
Note that it states that these totals will be placed elsewhere in the form, on line 103 for the Buyer side, and on line 520 for the Seller.

