They give the recipes to you, they are also online. You add natural conservants, so things don´t go bad. Well, some other stuff has a limited time that you can store it, but shampoo lasts for ages.
Also, the stores Müller, Rossmann and DM each have their own brand of cheap natural cosmetics (Alverde, Alterra etc), and their stuff is free from SLS, cones, parabens and other crap. I actually think that all these brands are actually manufactured by the same factory, and then packaged differently for each store, because the products are very similar and even the names and the packaging are alike.