I get your point but I can't get over the irony.
People were having fits about chinese e-liquid back in early cig-a-like days because they were making it with antifreeze. The antifreeze was pg.
You made the assertion that there wouldn't be an economic incentive to alter the ingredients given the relative low cost of the ingredients. The key word here is relative. To an American or European, perhaps it wouldn't be due to our overall economic wealth. But in countries around the world that stuff is not as inexpensive as one would think. Therefore, they do have economic incentives to substitute or adulterate the ingredients.
One area in which we can see this daily is in the equipment we use. The Wismec RX 2/3 is a fine example. The wire that goes from the battery terminal to the power button is too thin. It will break eventually, as mine did. I replaced the wire with a thicker gauge. Wismec could have used the thicker gauge to begin with but it was an economic decision not to do so. The savings per unit is so small it seems insignificant. However, combine that with the other areas of the mod that also used less desirable components, such as the screws, the metal for the battery connectors, etc. Once all is taken into account, now the savings add up to a few pennies. Now multiply that by tens of thousands. Again, maybe the overall savings is only $10,000, for sake of argument. But the companies producing these are making lots and lots of stuff, not just Wismec mods. Multiply that 10k by 100 products and now the amount is huge money by US standards, never mind Chinese standards.
Finally, the large manufacturers in China are probably in business for the long haul so they have to count every penny. But who is going to get into the Juice business? We see in the US a massive influx of people into the juice business, many of whom have no idea what they're doing. Many are playing it for short-term gains. Now think about China and who will be making the juice. It's not going to be Foxconn, that's for sure. It's going to be some shithead and his best friend mixing this shit in their bathroom. There is no way you can safely say it isn't true.
As for the vaping industry policing itself, do you really think for a moment some guy in Shanghai is going to give a flying fuck about we say on these forums? Ultimately, we are always taking a risk on consuming products that go into our bodies. Life is full of so many risks. However, there is a quantifiable difference in the risks we take. Would you rather take the risk with some company in the US that has some presence in the vaping community or with a totally unknown quantity in China, a country which is opaque to an extreme?