Measurement by Proxy: On the Accuracy of Online Marketplace Measurements


Alejandro Cuevas, Carnegie Mellon University; Fieke Miedema, Delft University of Technology; Kyle Soska, University of Illinois Urbana Champaign and Hikari Labs, Inc.; Nicolas Christin, Carnegie Mellon University and Hikari Labs, Inc.; Rolf van Wegberg, Delft University of Technology


A number of recent studies have investigated online anonymous ("dark web") marketplaces. Almost all leverage a "measurement-by-proxy" design, in which researchers scrape market public pages, and take buyer reviews as a proxy for actual transactions, to gain insights into market size and revenue. Yet, we do not know if and how this method biases results.

We build a framework to reason about marketplace measurement accuracy, and use it to contrast estimates projected from scrapes of Hansa Market with data from a back-end database seized by the police. We further investigate, by simulation, the impact of scraping frequency, consistency and rate-limits. We find that, even with a decent scraping regimen, one might miss approximately 46% of objects—with scraped listings differing significantly from not-scraped listings on price, views and product categories. This bias also impacts revenue calculations. We find Hansa's total market revenue to be US $50M, which projections based on our scrapes underestimate by a factor of four. Simulations further show that studies based on one or two scrapes are likely to suffer from a very poor coverage (on average, 14% to 30%, respectively).

A high scraping frequency is crucial to achieve reliable coverage, even without a consistent scraping routine. When high-frequency scraping is difficult, e.g., due to deployed anti-scraping countermeasures, innovative scraper design, such as scraping most popular listings first, helps improve coverage. Finally, abundance estimators can provide insights on population coverage when population sizes are unknown.

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@inproceedings {281350,
author = {Alejandro Cuevas and Fieke Miedema and Kyle Soska and Nicolas Christin and Rolf van Wegberg},
title = {Measurement by Proxy: On the Accuracy of Online Marketplace Measurements},
booktitle = {31st USENIX Security Symposium (USENIX Security 22)},
year = {2022},
isbn = {978-1-939133-31-1},
address = {Boston, MA},
pages = {2153--2170},
url = {},
publisher = {USENIX Association},
month = aug

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