I had never heard of either one so I looked them up...
A lot of their soaps seem identical except Basin's soaps are about half the size. So my guess is either they both order soap from the same company or both sites are owned by the same company, or Basin buys from Primal and cuts the bars in half. haha. I have no idea though.
You can buy primal essence soaps buy the loaf and then slice them yourself. And they sell wholesale. Another big seller in the upscale M&P market are gem soaps or rock soaps. Good luck. I would sell my self to the devil if i could open a shop. But for now I can dream. Keep us posted so we can live through you!