Online commerce, increasingly running on digital platforms, is subject to higher uncertainty and risk in transactions (e.g., fraud, opportunism) than offline commerce. To cope with this challenge, online commerce companies often use information systems to promote interactive communication between sellers and buyers. This study examines how such seller-buyer interactivity affects buyers' purchase intention in an online commerce context of accommodation sharing. In particular, we use text mining techniques to analyze guest reviews and host responses on Airbnb. Our analysis suggests that not only the quantity but also the quality of the response messages matter: potential guests' purchase intention increases with the relevance and richness of the host's responses as well as their volume. Further, we find a notable nonlinearity in the quantity effect that the volume of host responses significantly affects guest purchase intention only when it is large enough. Making sufficient responses, the hosts could enjoy complementarity between the quantity and quality effects of their responses; otherwise, the relative richness of their responses becomes more important.