How is Nick Carraway, from The Great Gatsby, shallow?

It could be argued that Nick's shallowness is exemplified by his own aspirations and self-image; he purchases books on finance and wealth in an effort to become "that most limited of all specialists, the 'well-rounded' man," and he considers himself to be a great judge of character, "snobbishly repeat[ing]" that he possesses a disproportionate amount of the "fundamental decencies" that others presumably lack.

Finally, his shallowness can be seen in the quickness with which he dismisses his own doubts about Gatsby's background.  Skeptical to the point of "incredulity" when Gatsby recounts his life story in chapter four, Nick abruptly determines that "it was all true" as soon as Gatsby produces a medal and a photograph. Only minutes earlier, Nick could barely "restrain [his] incredulous laughter" at Gatsby's preposterous past, but the photo of Gatsby with a "cricket bat in his hand" is all it takes to convince him that he indeed lived the romantic and heroic life of an adventurer, soldier, and scholar.  

In short, Nick Carraway seems so blinded by Gatsby's trappings of wealth and romance that he willfully ignores his moral transgressions, and this could be seen as "shallowness" on Nick's part.