...how do you make the skin tones look the same if you were to take the face off of pic a and layer it over pic b? I tried the smudge function and blur function but neither did it as cleanly as I was hoping. Any ideas?

I would first try to match the both layers with brightness and contrast, and with saturation (and VERY slight hue changes, if necessary) as close as possible. Depending on the pictures, you might have to "over light" it with a higher contrast level to make it look real and hide not matching things, but this is usually the last thing I do, since I try to keep the pictures as close to the original ones as possible. Yes blur and smuge are pretty useless for this, unless towards the end of the project, to touch up and clear out little bits and pieces, but always keep the "pressure" levels in the option windows as low as you can. I usually take my time and use the cloning tool while keeping the pressure settings low.

I like to zoom in and airbrush pixel by pixel. It is lengthy but the out come is very good if your skills are up to par.