Remember, the Bingley sisters, especially, were eager to raise themselves in society, so I'm sure Mrs. Hurst would have chosen a man whose social credentials were at least a step above hers who would be glad to take her for her money. (There have always been members of "good families" who had less money to support their lifestyle than they felt they deserved!)

When the Omniscient Narrator says that Mr. Hurst "merely looked the gentleman", IMO she is saying that the guests at the Assembly could tell by looking at him that he belonged to the gentry, not a lower class. Remember how terribly sensitive they were to small class differences in those days!