Depending on what game engine or 3D software package you use, the way in how these programs handle normal maps are often different. In programs such as ZBrush and xNormal, there are settings allowed for exporting normal maps to different target platforms. That is great, but what is the difference between normal maps exported for say 3DSMax vs. Maya, or UDK vs. marmoset?
If the normal map you bake out are showing seams and artifacts, a quick way to fix this is to simply inverting the Green channel in the R(G)B stacks inside of Photoshop.
This is a maya screengrab of a creature mapped with normal map baked out using the 3DS max setting from ZBrush. Notice the seams on the edges and borders, not to mention all the details are sunk in, instead of relief.
R|X+ G|Y- B|Z+
A quick and easy way to fix it, instead of using any plugin or filter. Go into the Green channel > Select All > Invert