the seller would only have been able to post Wed at the earliest, and not everyone goes to the PO everyday. how was it being sent? i sold something on ebay recently that took 10 days to arrive! i posted the same day they paid, so wasnt even my fault.
He will probably send it 2nd class then, and pocket the change lol. You will probably get it sometime next week. I wouldnt hassle til next week either, maybe a polite "when do you think my parcel will arrive?" on Monday.