I have modeled the right halve of a character and have duplicated it to make the left halve. My problem is that there is a harsh seam between the two models. Here is a screen shot of the image: http://imgur.com/rDckjvX.
The problem here is that there are two sides. Once you merge the objects this should correct (and if not it will be less obvious). It will definitely have something to do with the direction of the face normals so if the seam is still there once you have combined the two sides and merged the vertices running along the middle you may need to soften the face normals.