Below is how our system handles delivery fees within Japan (from the seller to our warehouses)

Closing price	Delivery method
1-9,999yen	The cheapest delivery method
10,000yen or higher	The cheapest delivery method "with a postal insurance"

So, if the closing price for an auction marked with "Free delivery" is 10,000yen or more and if the seller does not indicate that the item has postal insurance, we will switch to a delivery method that includes postal insurance.