@DaveP , I DIY and shop at several of the main online vendors. Someone mentioned ethol Alcohol and needing to let the mix "air out" before storing it to steep. All mine, regardless, air out overnight and steep for a minimum length of time, which is rather long. That is just me.
Anyway, I thought to check which flavors I have that have alcohol in them. What I ran into was that one vendor said the flavor had alcohol and another vendor said it didn't. Then, I went to the manufacturer's website to get their story. I tend to believe the manufacturer unless they don't say, which then I stop buying their flavors.
As a DIYer, I think it is good to know what is in the flavorings and that is really all that I am doing. I did notice that one brand of juice seemed to have more strange chemicals that the other brands. Remember, I am only checking the flavors that I have in my recipes, so I could be off base about claiming any one brand is worse than another.
I used to go into vape shops to taste test and talk shop. I did notice that the flavor, as tasted in the shop, was not the same as when I finally used it. I found juices online and that is where I just got into the airing and steeping practice. I was basically buying in groups to use 2-3 months down the road. That is when I tested the juice and determined whether I liked it or not.
I gotta say that doing trial and error with store bought juices, 2-3 months after purchase, got expensive. DIY is much cheaper and I have a much better handle as to what is going in my tank.
I have also seen some pretty unsanitary shops that made juice on-site. DIY is better.
Hope helps