  Dark web marketplaces have been a significant outlet for illicit trade,
serving millions of users worldwide for over a decade. However, not all users
are the same. This paper aims to identify the key players in Bitcoin
transaction networks linked to dark markets and assess their role by analysing
a dataset of 40 million Bitcoin transactions involving 31 markets in the period
2011-2021. First, we propose an algorithm that categorizes users either as
buyers or sellers and shows that a large fraction of the traded volume is
concentrated in a small group of elite market participants. Then, we
investigate both market star-graphs and user-to-user networks and highlight the
importance of a new class of users, namely `multihomers' who operate on
multiple marketplaces concurrently. Specifically, we show how the networks of
multihomers and seller-to-seller interactions can shed light on the resilience
of the dark market ecosystem against external shocks. Our findings suggest that
understanding the behavior of key players in dark web marketplaces is critical
to effectively disrupting illegal activities.
