Both walmart and target have super return policies. As long as you have that original receipt they will take it back
Finding the right foundation is super hard, it took me forever to find the one that just disappears into my skin. I caved and bought Benefit 'Hello Flawless' liquid foundation since it made me so happy, I wear it everyday (and for me that everyday use justifies the higher cost, I'm still on my first bottle from April).
If you have tricky skin tones water based foundations allow for a little translucence, thus letting your natural skin tone to come through a little. Heavier silicone ones, though giving a more 'flawless' look have much less wiggle room, in my experience, in terms of color.
I know covergirl.com has a whole skin tone matching quiz to go through and it then puts a little pink dot next to every product that would complement your skin tone on the website.