In a range of contexts, pairs of interacting individuals arrive at collective decisions by comparing their confidence in their judgements. This tendency to evaluate the reliability of information by the confidence with which it is expressed has been termed the ‘confidence heuristic’. In this study, we tested two fast and frugal ways of implementing the confidence heuristic in the absence of interaction: either directly, by opting for the judgement made with higher confidence, or indirectly, by opting for the faster judgement, the latter exploiting a widely known inverse correlation between confidence and reaction time. We found that the success of these heuristics depends on how similar individuals are in terms of their abilities and, more importantly, that for dissimilar individuals such heuristics are dramatically inferior to interaction. Interaction allows individuals to alleviate – but not fully resolve – their differences in ability.