Micro-influencers—content creators with up to 100,000 followers—play a key role in influencer marketing. This qualitative study, based on 30 in-depth interviews with Spanish micro-influencers, examines their work processes and relationships with the three main actors in commercial collaborations: agencies, brands, and micro-influencer platforms. Findings show micro-influencers’ strong motivation to engage in paid partnerships. Among the three actors, platforms emerge as crucial allies, providing broad opportunities to collaborate with brands across sectors. Yet, registration often requires follower and engagement thresholds unattainable for smaller creators. Platforms offer clear conditions on content, timelines, and compensation, but interactions tend to be impersonal, with rigid publication and content rules. By contrast, direct collaborations with brands are more flexible and personalized and often lead to repeat partnerships. For those with smaller audiences, they remain the main entry point into commercial activity, though many participants called for clearer collaboration terms.