INTRODUCTION: Drug sellers are often represented as morally bereft actors and as being, in part, responsible for North America's overdose crisis. In Canada and the United States, drug sellers selling fentanyl and fentanyl-adulterated drugs have been charged with manslaughter when their clients fatally overdose, representing a retrenchment of drug war tactics. However, targeting drug sellers for drug checking interventions may have potential for reducing fentanyl-related harms. This study explores drug sellers' negotiation of and engagement with drug checking technologies in Vancouver, Canada.

METHODS: Rapid ethnographic fieldwork was conducted from November 2018 to January 2019, including 26 semi-structured interviews with people who tested their drugs at an overdose prevention site to examine perceptions of the efficacy of drug checking. As drug sellers were also using the drug checking services, we specifically examined their perceptions of drug checking and the market aspects of the overdose crisis. Data were analyzed using Nvivo 12 and interpreted drawing on the concept of structural vulnerability.

FINDINGS: Drug sellers accessing drug checking services were concerned about the safety of their customers, and drug checking was one way of reducing the likelihood of harm. Drug sellers were embedded in the community, thereby, enmeshing practices of community care and ethics with the selling of drugs. When they had access to drug checking knowledge, sellers were able to modify risks related to the fentanyl market, including tailoring drugs sold to clients, returning dangerous batches and modifying fentanyl in order to make it safer to consume.

CONCLUSIONS: Our findings reposition drug sellers as embedded within their communities and demonstrate their potential role in alleviating the dangers of the volatile fentanyl market. Policies that target people who sell drugs, particularly murder or manslaughter charges, are likely to make the crisis worse, and serious consideration should be put into harm reduction approaches with drug sellers.