We study the impacts of `humanising' AI-enabled autonomous customer service agents (chatbots). Implementing a field experiment in collaboration with a dual channel clothing retailer based in the United States, we automate a used clothing buy-back process, such that individuals engage with the retailer's autonomous chatbot to describe the used clothes they wish to sell, obtain a price offer, and (if they accept the offer) print a shipping label to finalize the transaction. We causally estimate the impact of chatbot anthropomorphism on transaction conversion by randomly exposing consumers to exogenously varied levels of chatbot anthropomorphism, operationalized by incorporating a random draw from a set of three anthropomorphic features: humor, communication delays and social presence. We provide evidence that anthropomorphism is beneficial for transaction outcomes, but that it also leads to significant increases in price elasticity. We argue that the latter effect occurs because, as a chatbot becomes more human-like, consumers shift from a price-taking mindset into a fairness evaluation or negotiating mindset. We also provide descriptive evidence suggesting that the benefits of anthropomorphism for transaction conversion may derive, at least in part, from consumers' increased willingness to disclose personal information necessary to complete the transaction.