"He may have a queer history, and he may not have told us all of it, but Ajo is honest.
I'll vouch for him!" "So will I, my dear," said Uncle John.
"That is more than I can do, just at present," Arthur frankly stated.

"My opinion is that his preposterous offer is mere bluff.

If you accepted it, you would find him unable to do his part." "Then what is his object ?" asked Maud.
"I can't figure it out, as yet.

He might pose as a millionaire and a generous friend and philanthropist for some time, before the truth was discovered, and during that time he could carry out any secret plans he had in mind.

The boy is more shrewd than he appears to be.