An excellent meme, via Purple Pen ...
Which authors have you read more than ten books by?
Mine are (or those I can remember thus far, roughly in the order in which I read them) ...
Elyne Mitchell (particularly her brumby books. (Brumbies are wild horses.)
Ruby Ferguson (of the "Jill" pony books)
Zane Grey (and probably several other writers of Westerners I've now forgotten)
Patrick O'Brian (and probably several writers of war novels of varying eras whose names I've forgotten)
George Macdonald (Yes the Flashman series; I'm bring brutally honest here - and I was only about 13)
Dorothy L Sayers
Kerry Greenwood (on whom I posted here)
Marele Day (a rather good Australian writer of feminist detective stories))
Obviously, the way to sell lots of books is to write long series of detective novels or thrillers, or at least that is what this list would suggest.