I had that happen a couple of times.
What I did is learn that talking to a person always helps. Instead of bidding on the item I called them and asked them specifically, "can I pay you "X" amount for the item, they said yes, it will be an addtional $10 for shipping I then say ok here is the address. You have to sound serious and not wishy washy on the phone. I was dealing with a business, not an individual selling an item.