Ducks must ship in post office approved carriers. It doesn't matter whether there are 2 ducks or one, they need the same carrier. Shipping live adult birds is expensive. It is only worth it to ship adults if the birds are top quality and you must have them.
An adult WH should weigh about 5...
He was right about one thing. It would cost you abut $100 to ship a pair of adult ducks.
I have 3 breeds from Holdeerread and they are all excellent quality. I've never seen his Calls, so can't say from personal experience, but it is hard to imagine that they are junk.
The Welsh Harlequins...