Thanks to both of you for looking. You hit the same problems as I did on this one, and frustratingly official documents aren't any help. While William was still in Durban, one daughter's baptismal record gave his occupation as "Manager of store," and his death notice gives his occupation simply as "Retired merchant," so neither are very helpful. One of his brothers was manager for Curtis & Co. in Jo'burg selling clothing, another worked for T.W. Beckett (possibly as a commercial traveller) in either Pretoria or Jo'burg, for a little while, before haring off to China, and the third ended up as a men's wear salesman in Edmonton, Canada. On the basis of this, I'm guessing that William was in a similar line, but it would be far better to have actual proof!