In The Great Gatsby, why does Nick suspect that Gatsby isn't telling the whole truth about himself?

Because people
keep hinting that there's more, For example,is suspicious of . Gatsby himself sometimes
contradicts his own story.  For instance, he tellshe is the son of wealthy Midwesterners, but
later says he comes from San Francisco. Through Gatsby Nick meets Wolfsheim, a mobster - seems
like strange company.  there are rumors of "drug stores" that are selling bootlegged
liquor.   when he confronts Gatsby in Nick's presence challenges Gatsby's claims to such things
as having attended Oxford.