But the buyer insists there is no need for a deposit, that using an escrow is enough. The problem is I don't know the exact price of the shipping until I'm at the post office with the product already purchased ready to be sent, and we don't know what the price of Bitcoin in A's currency will be at the time of purchase. There could be a day or two between the time he sends Bitcoin to the escrow, and the time the product is bought.
What the deposit for, by the way?
There must be an estimation cost for any products like per kilogram or anything which lets you know without need to bring the product to post office or any shipping company office.