a liquid only fast is a good concept but it has to be executed correctly. drinking fruit juices and smoothies are going to still be digested by the body and they have a lot of sugar. so the detoxing is going to be minimal
so although i like the concept you really should only drink non and low caloric drinks like water, water with electrolytes, maybe some greens powder, etc.
you should check out my Ebook in my signature, i go over all that stuff