Source? If we believe Nicolas Christin's estimate of $15 million in revenue, and use your number for the average revenue per seller, then there would only be 42 sellers on the site. That is obviously not the case. Christin found 560 unique sellers and 112 "core" sellers who were on the site for the whole 6 months that he scraped it. There are a lot of small time and short lasting sellers on SR. Over half don't last longer than 3 months. (See the paper below) If we assume that there are always about 200 sellers on the site, and the ones who leave get replaced by an equal number of newcomers, then the average yearly revenue per seller is $75,000. Note: that's revenue, not profit. https://www.andrew.cmu.edu/~nicolasc/publications/TR-CMU-CyLab-12-018.pdf