Social media has become a widely used marketing tool for reaching potential customers. Because of its low cost, social media marketing is especially appealing to customer-to-customer (C2C) sellers. Customers can also benefit from social media marketing by learning about products and by interacting with sellers in real time. However, a seller's marketing microblogs may backfire on her for dominating the social space. Defining the marketing popularity as the average number of likes each seller receives per marketing-related microblog and defining the marketing aggressiveness level as the proportion of her marketing-related microblogs, this paper empirically quantifies the optimal level of marketing aggressiveness in social media to achieve the maximum popularity. We gather the data from China's largest microblogging platform, Sina Weibo, and the sellers in our sample are from China's largest C2C online shopping platform, Taobao. We find that the empirical relationship between the marketing aggressiveness level and the marketing popularity follows an inverted U-shape curve, where the optimal level is around 30%. In addition, we find a saturation effect of the number of followers on marketing popularity after it reaches around 100,000. Our findings imply that social media market-* We thank the helpful comments from the participants of the seminars at