I'm always glad to hear of someone questioning the quality and/or purity of essential oils. There are many options out there and it's often difficult to distinguish the truth from the marketing hype. The following is a summary of my response to a recent inquiry.
Whenever possible I use oils from wildcrafted plants growing in their indigenous environment. The best chemical combinations come from plants growing as God intended them to, with the environmental conditions true to nature without interference from humans. Certainly these could be considered to meet the requirements of "organic" but the reality is that they may not be labeled as such. My second choice is organic. Organic has very obvious benefits, but the reality is that in order to obtain an organic certification one must introduce some level of human controls into the growing process. This disruption may or may not interfere with the chemical profile of the finished product.
There are other important considerations in determining the quality and purity of the oils. One must understand the distillation or extraction process to determine how this impacts the presence of any impurities in the final product; as well as how this impacts the presence and ratio of specific constituents. Gas Chromotography (GC) is often used to characterize the chemical composition of an oil. The results of which are quite informative to those who understand how to read them. I rely on these reports for analysis and comparison, having performed GC tests myself while working in a lab.
Three key items are important for anyone using essential oils: the latin (or binomial) name, the extraction process, the region of origin. I recommend not using any essential oil that does not provide this information clearly in the labeling. One doesn't need a chemistry degree to verify that the oil is the correct genus and species, has been properly prepared, and originates from a plant in its natural growing environment.