The bluestreak cleaner wrasse, Labroides dimidiatus, can be found on coral reefs throughout the Indo-Pacific. These little fish live in small groups on cleaning stations, and offer a cleaning service to other reef fish by eating the surface parasites that live on the clients’ skin. All is not as harmonious as is appears, however. Clients want cleaners to eat the ectoparasites but cleaners prefer to feed on mucus and scales – which is harmful and painful for the client. The cleaner-fish client mutualism is therefore a wonderful model system for exploring how conflicts of interest are resolved and for identifying the mechanisms that support cooperation in real-world interactions.