With the ever-growing popularity of sharing economy platforms, complementors increasingly face the challenge to manage their reputation on different platforms. The paper reports the results from an experimental online survey to investigate how and under which conditions online reputation is effective to engender trust across platform boundaries. It shows that (1) cross-platform signaling is in fact a viable strategy to engender trust and that (2) its effectiveness crucially depends on source–target fit. Implications for three stakeholders are discussed. First, platform complementors may benefit from importing reputation, especially when they have just started on a new platform and have not earned on-site reputation yet. The results also show, however, that importing reputation (even if it is excellent) may be detrimental if there occurs a mismatch between source and target and that, hence, fit is of utmost importance. Second, regulatory authorities may consider reputation portability as a means to make platform boundaries more permeable and hence to tackle lock-in effects. Third, platform operators may employ cross-platform signaling as a competitive lever.