To answer your questions I have to answer #2 first. Jena is right – there are a limited number of distilleries, D. Gary Young owns 1/3 of them. The products distilled to make EOs are like the contents of tea – they can be distilled multiple times but each time you do so the product you get is progressively weaker. Companies like doTERRA and Young Living only take the 1st distillation which is the strongest and most pure. They label their product therapeutic grade and 100% pure because they have run it through a mass spectrometer and have calculated the constituents in each bottle. Young Living actually refuses to sell any bottle of EO that does not meet their requirements for purity. Less expensive companies use the 2nd, 3rd, and even 5th and 6th distillation. They also dilute their products before marketing them. So it is important to know about the company you are buying from and what distillation they use. Not all distillations are equal.
Essential oils are generally extracted by distillation, often by using steam. Other processes include expression, solvent extraction, sfumatura, absolute oil extraction, resin tapping, wax embedding, and cold pressing. They are used in perfumes, cosmetics, soaps and other products, for flavoring food and drink, and for adding scents to incense and household cleaning products.