@ jane

The inventory valuation method (average cost, FIFO, LIFO, etc) has nothing to do with the requirement to account for all costs to get an item on hand and ready for sale as the item cost.

Outside costs, third party shipping, customs, etc require a work around in all versions of QB.

enter the bill for the items/qty received and enter the cost per item as you know them at that time.  That stocks the items with qty and cost.

When you pay additional costs, shipping customs, etc do just what you are doing now, post them to a clearing account.

Then edit the original bill
1. add a portion of the total amount in the clearing account to each item total cost
2.  In the account details part of the bill, select the clearing account, and enter the full amount in that account as a negative number.  The total of the bill will not change, save an clck through any warnings about payments being applied

QB will then, go back and adjust the cost per item on that purchase to reflect the increased costs.  And if any have been sold in between the receive date and the date you added the costs, QB will automatically make an adjustment entry in both inventory asset and COGS only for those items sold, bringing COGS up to date for the new cost per item.  That adjustment will show in a detail report for COGS as having a Bill as the source of the adjustment.