what happened...for the pros

A buddy of mine just had a B and G of a boat done. This was about 3 months ago. Yeah its one of those common multi sails with the waves. I am sure you have seen them before. Its had some good time to set in and he took really good care of it for the first few weeks. It had faded as expected from the super black to a grey and black. The tattoo looks great except for one small issue. The artist started from one side and worked his way across. The side he started on is very dark. Looks great like it should. But on the other side of the boat, it still looks good but its less dark. I know this is hard to picture and even if you saw it you wouldn't take a second look, but it almost seems like the artist ran out of ink and used a different cap or something that might have been watered down or something. You can put you hand on the tattoo and almost draw a line between the sides and see how one side almost looks like it was done with different ink. The tattoo is far from done so I am sure that the artist can always make something darker, right? He told my buddy that his body doesn't take ink well. I have heard this about myself before as well with no problems. My friends tattoo by no means looks bad, but could look more vivid we think. The both of use are rather hard on the art. I am pretty honest with him, and the same goes from him with me. I told him that he should tell the artist that it looks a little lite. He doesn't want to offend the guy and hopes that the artist notices this in his next session and touches it up. He told him that it would need to be touched up after his first sitting. All and all it looks good and if you saw it you would probablly say it looks fine, but we think it should be perfect. I mean it is going to be on him forever....right?