Well,, while that infographic in the first post you made would confuse almost anyone, no, the likelihood of a professional liquid maker using a product that a) is more expensive than PG or VG and also is completely different as far as viscosity, color, etc and b) is likely to kill off the customer base the vape retailer is so carefully nurturing.
C) Legit business don't do this. OF ANY SORT, and that includes THC, CBD AND nicotine. These business all have licenses, to some degree or another and of varying types in different states, but t hey are ALL required to confirm to various health code standards, The use of Vitamin E oil in ANY concentrate would NOT confirm to health code standards.
SHOULD a business be insane enough to try it (they aren't) the source of the outbreak would be traced back to that retailer pretty quickly and they'd be closed, accused of manslaughter at best and murder at worst.
I'm not saying all ejuiice (of any time) is the same, completely free of any impurities or anything else. There are standards of acceptable impurity in any manufacturing type of deal.
However, I would say the LEGIT e-cig market (for anything) is about as safe as it is going to get. They're all under a lot of scrutiny these days.
The type of person who wants to make a quick buck by diluting THC (very expensive vaping concentrate) with something that will KILL its customers strikes me as a black market operation. Black markets often do not tend to think of their customers as a valuable "base" as the likelihood of dying via overdose, the dealers themselves being locked and caught up, are the types to do this. They are thinking of a quick buck NOW and what they can do with it, and who they kill along the way is not of particular interest to them. They can move on, to the next market, the next substance, etc..
This is why I say legalize everything, it greatly REDUCES the black market. It does not eliminate it completely. There are always folks who are gonna want to pay slightly LESS with MORE RISK for Mexican field weed, even though I'm ready to bet that gram for gram, if potency were tested, legal stuff is actually better value.
I say let Darwin care for those folks. However, ,we can have a sane society for those intelligent enough to seek one.
TL

R YOU ARE FINE WITH ANY TYPE OF VAPE IF REMAINNING WITHIN THE LEGAL MARKET except that CBD is a "Supplement" in some states and sort of unregulated. It's unlikely to kill you, it's label may claim FAR more potency than it actually has.
People starting a company though sort of tend to not want to kill off customers on purpose. There is a lot involved with starting a business much of it unpleasant.
Anna