I just made a best offer for an item which included free shipping. The seller accepted but then added shipping costs in the invoice.
For example, the item was originally $25 with free shipping, which I then offered $20. The seller then accepts but adds on an extra $2.50 for shipping. Is that fair?
If it had the option of free shipping and you selected it when checking out/purchase than the seller has no right to add $2.50 postage.