  Community-based question answering (CQA) services are facing key challenges
to motivate domain experts to provide timely answers. Recently, CQA services
are exploring new incentive models to engage experts and celebrities by
allowing them to set a price on their answers. In this paper, we perform a
data-driven analysis on two emerging payment-based CQA systems: Fenda (China)
and Whale (US). By analyzing a large dataset of 220K questions (worth 1 million
USD collectively), we examine how monetary incentives affect different players
in the system. We find that, while monetary incentive enables quick answers
from experts, it also drives certain users to aggressively game the system for
profits. In addition, in this supplier-driven marketplace, users need to
proactively adjust their price to make profits. Famous people are unwilling to
lower their price, which in turn hurts their income and engagement over time.
Finally, we discuss the key implications to future CQA design.
