You have to pick an artist that knows what they're doing. Sometimes self taught artists can instinctively develop the know-how because they have less to unlearn than the professionally trained(art as a discipline in schools tends to default to white-canvas-everything, though that's slowly changing), but even they can mess up. What you want is someone who can work from any shade as a starting point, who also understands colour and lighting. That kind of knowledge overlap with tattooing is rare, and it ain't cheap.
Really great thread. Peace and blessings to the City of Ink crew.