In the guestworker system deployed in the Mauritian export factories, where migrants come to work on temporary contracts, employers and their labour brokers constantly need to hire new workers. And in this permanent renewal of the workforce, recruiters express their preferences for specific nationalities of employees and their disdain for others. Through in-depth interviews conducted with both employers and labour brokers, this contribution explores the production of a ‘knowledge’ on workers, a taxonomy that attributes certain qualities to certain people in the ranking of the ‘best worker’. The article contends that racialised assumptions on work ethic are intimately combined with a logic of profit maximisation, both dimensions being mutually constitutive of taxonomies at work.