It should list exactly one ingredient (e.g., Lavandula angustifolia ). If it says "fragrance" or "perfume," it’s synthetic.
The search results are often cluttered with "Fragrance Oils" or "Scented Oils" that aren’t actually safe for topical use or therapeutic diffusion.
Some third-party sellers dilute their oils. I always look for a GC/MS test report (a chemical breakdown) in the product images or description to verify purity.
You can often get 4oz bottles for the price of a 15ml bottle elsewhere.