Contract cheating occurs when students outsource assessed work. In this study, we asked experienced markers from four disciplines to detect contract cheating in a set of 20 discipline-specific assignments. We then conducted a training workshop to improve their detection accuracy, and afterwards asked them to detect contract cheating in 20 new assignments. We analysed the data in terms of sensitivity (the rate at which markers spotted contract cheating) and specificity (the rate at which markers spotted real student work). Pre-workshop marker sensitivity was 58% and specificity was 83%. Post-workshop marker sensitivity was 82% and specificity was 87%. The increase in sensitivity was statistically significant, but the increase in specificity was not. These results indicate that markers can often detect contract cheating when asked to do so, and that training may be helpful in improving their accuracy. We suggest that markers' suspicions may be crucial in addressing contract cheating.