One Clue the Victims Never Considered

The guests believe that U.N. Owen owns the island until Rogers tells them it's been leased for the week.
So, once they discover that Mr. Owen is one of the guests, none of them consider this: who is successful enough to pay for the rental of a mansion on an island?
- Vera is a secretary, so not her.
- Mr. & Mrs. Rogers are servants who, even with an inheritance from the woman they killed, still need to work.
- Blore is a policeman, so not him.

That leaves the following possibilities:
- a successful doctor (Armstrong)
- a successful judge (Quincannon/Wargrave)
- an explorer who might have discovered diamonds in his exploits (Lombard)
- a rich playboy (Starloff/Marston)

So, while there may have been ten guests, there really were only four people with the financial potential to pull this off... assuming, of course, that everyone is who they say they are!