More than 85% of UK non-EU export value is facilitated by customs agents, yet little is known about how firms organise and adjust these relationships. Using transaction-level UK customs data from 2009 to 2019, this paper provides novel evidence on trader-agent relationships. We document a highly concentrated and skewed network structure: most trader-agent links are short-lived and low value, while a small number of persistent relationships account for the majority of agent-mediated trade. We show that agent use reflects distinct strategic motives. Firms are more likely to rely on agents when entering new markets or introducing new products (exploration), but these exploratory relationships are shallow and short-lived. In contrast, when firms trade in markets aligned with agents’ established expertise (exploitation), relationships are deeper and more persistent. Finally, exploiting the 2016 Brexit referendum as a policy uncertainty shock, we show that EU-exposed firms reorganise and deepen their reliance on customs agents.