If special shipping instructions were asked for after the auction, and adhered to without question by the seller even though it was at extra cost (they may have already bought their standard shipping materials at reduced cost in bulk) then I can't possibly see how one shouldn't be willing to pay the extra.
They sent without asking for the extra payment first, and with no guarantee that they wouldn't lose out by not being covered - whatever their previous feedback says this sounds like an excellent and responsible seller to me...