A directs B his solicitor to sell his estate by auction and so employ an auctioneer for the purpose ...........

A directs B, his solicitor, to sell his estate by auction, and so employ an auctioneer for the purpose. B names C, an auctioneer, to conduct the sale.

C is a sub-agent, and A’s sub-agent for the conduct of the sale

C is not a sub-agent, but B’s agent for the conduct of the sale