3rd question.

In that same message it states:

Free postage option: Choose if you want your buyer to pay for the label, or offer free postage and cover the cost.

Why does this cost the seller more than it costs the buyer? This is the same label, costing the same amount regardless of who pays.
e.g. 100g LL by SD, buyer pays £2.70, if choosing free postage/seller pays, the cost is £3.42