A good vendor will know not to use butter flavorings that containt Diacetyl which is what is commonly found to be the source of popcorn lung. I vape MBV's vanilla custard and they are very proactive about what goes into their juices. A month or two ago there was a big uproar about vaping certain type of cinnamon flavors and they quickly pulled all their cinnamon flavors. Once everything was cleared up they resumed selling the okay to vape cinnamon flavors. Some vendors are in it for money only, others actually care about their customers.