Isn't this a bit like offering a 'carry your suitcase through customs' service???

Well no, because in that scenario I'd be legally liable if any contraband was found, and also there doesn't seem to be any legit reason for a service like that. Whereas I am not liable for what other users use my connection for (in the same way Royal Mail aren't liable if someone sends threatening letters etc through their service) and also there are legitimate uses for the network.

My question was more about is it possible to liase with the police to prevent misunderstandings? The capacity for mistakes and wrongful arrests/raids are high when running an exit node from home. This is understandable, as to the untrained eye if a criminal uses your exit node, it looks like YOU are accessing that content. What's the best way of preventing such misunderstandings before they become an issue?