Let us keep it seen as a misunderstanding.

I do not know about your private messages, so take this as another neutral remark:
asking for spedition/shipping cost is definitely not a 'buying confirmation' but only show of interest.
Of course seller will deal with others. So only after confirmation from seller to buyer I would see it as 'deal confirmed'. (even then seller may make the deal perfect for the person paying first. something all parties should be informed about).