He should lighten up! It just happens like that sometimes.
I agree, contact the auctioneer to mediate on your behalf, but I don't think you have to worry about it too much. I think you offer to take the ewes back and return his money was more than generous.
We had a similar experience a few years ago - we bought some barren ewes with the idea of sponging them, lambing at Christmas and selling as couples in January. Two ewes lambed while the sponges were in!
Never even occured to us to get het up about it.