Prosocial exchange systems like Streetbank.com support sustainable consumption by promoting giving, lending, and skill-sharing. A study analyzed 5053 acts of offline exchange over 4.5 years and found that reciprocity is rare and often involves different types of exchanges. This means that not all exchanges are based on the expectation of receiving something in return. Designing these systems should not rely on reciprocity, and efforts to encourage it should make exchange patterns visible.