‘Grey corruption is where legal favours are traded amongst a select group, and where those favours incur external costs. Because this type of corruption is hard to observe in reality, we implement a laboratory experiment that captures the fundamental process of implicit back-scratching that underpins grey corruption. We test whether making transparent the identity of the those involved in the grey corruption, by publishing their photos, reduces grey corruption. Unfortunately it does not. While there was some effect on reducing the amount of grey corruption, photos also helped identify potential ‘partners in crime. The process of finding potential back-scratching partners was more rapid, and more likely to occur between experimental subjects with more similarities. The main policy implications is that sometimes transparency can backfire when it comes to anti-corruption efforts. Instead anonymity could be helpful. For example, political donations could be made anonymously through a central clearing house so that they cant be used as a signal to help coordinate favours between vested interests and political parties. Committees that decide government contracts could be secret, so that potential bidders do not know who to lobby to seek favours. These results clearly show the limits of transparency in combatting grey corruption.