If you are dealing with a fairly large producer, they will tell you on the label, or...
...on their advertising.
I use Molina vanilla blend. I got off the boutique-vanilla bandwagon years ago. The madagascar, etc., is wonderful, but too pricey for me. I use a lot of vanilla, and Molina is CHEAP, available in any market catering to mexicans here in Phoenix, and it tastes just fine to me and my family. Vanillin is a natural compound found on the outside of vanilla pods. It is also synthesized and accounts for about 70% of the vanilla used in manufacturing.
Ever since a cheap, store-brand vanilla won CI's testing, I stopped buying the expensive stuff.
Michael