More about those scents.
Essential Oils tend to have the same concerns. Lavender is a good example, there are a dozen types again, from light and floral to a more earthy. Lavender from France tends to be weaker than Lavender from Bulgaria, therefore, you would use less of the Bulgarian Lavender. If you aren't sure which type to get, stick to a blended Lavender, such as a 40/42. A friend of mine has noticed that one scent she gets from one supplier A is exactly the same scent from supplier B, but of a much lower strength. I know that I have had to double my Patchouli fragrance amount from a couple of years ago.
When you find that perfect scent, keep it. Some suppliers will offer samples, and even if you had to pay for a sample pack, it would be worth it.