From the passage, the reader can infer that the clerk is eager to please and attentive to Voldyrev, likely due to the perceived power and status that Voldyrev holds. The clerk's transformation from being reserved to lively and affable suggests that he recognizes Voldyrev's importance or potential influence. His demeanor, which includes smiling, bowing, and engaging in small talk, indicates that he is trying to make a good impression and maintain a favorable relationship with Voldyrev. Additionally, when Voldyrev gives him a rouble, the clerk's reaction—keeping his smile and receiving the money enthusiastically—implies that he may be motivated by an expectation of reward or appreciation for his service. Therefore, the best inference would be:
He acts with greater kindness because he eventually realizes who Voldyrev is.