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Our inventory is fast moving and keeps on changing every 15 minutes or so. We listed 1 item with 1 quantity and a shipping fee of 1.99. After a few hours we increased the quantity to 5. Now, when someone purcahses 2 or more copies of this item, they are only charged a shipping fee of 1.99. Are we missing anything here?
If you list a single quantity item, the AdditionalShippingServiceCost is defaulted to 0 and carried forward when you revise the item to be multi-quantity. Also if you specify AdditionalShippingCost when listing a single quantity item, the value will be ignored. SYI also allows you to specify AdditionalShippingServiceCost only if you are listing with quantity > 1
The following workaround might be good for situation -
1. List the item as multi-quantity item so that the AdditionalShippingServiceCost field is recorded
2. Use ReviseInventoryStatus to revise the quantity to 1 as soon as the item is listed.
If you get stock in the future you can update the quantity on the eBay listing (using ReviseInventoryStatus). The AdditionalShippingServiceCost field will be emitted and the original values you supplied will be used. This workaround eliminates the use of ReviseItem call and allows you to work with the light-weight ReviseInventoryStatus call.