Find a brand and supplier you trust and stick to them.
Whether it’s a nationwide legalized brand or a grey or black market operator you trust, your supply chain is only as reliable as the people in it. Support good people who are willing to put principle over profit. The cannabis and mushroom markets have been illicit and unregulated for generations, and problems with cannabis or mushrooms being ‘spiked’ or contaminated maliciously, or for greed, is extremely rare, especially compared to the business in other illicit substances. Failed or toxic hardware is more likely than toxic vape juice.
With that in mind, you should inspect cartridge/hardware quality.
Vaping is habit-forming, and if the cartridge is not of good quality, you may end up repeatedly inhaling small amounts of overheating plastic or extra wick material. There’s a much higher likelihood the hardware being accidentally harmful than someone intentionally making or distributing impure cannabis oil.
That said, after you inspect a new cartridge, inspect the oil.
Understand as well that no cartridge is 100 pure marijuana. Liquefying and extracting weed to the point that it can be vaporized requires solvents (CO2 being one of the most common).
If you suspect that a product might, for whatever reason, be unsafe, stop using it immediately. Trust your own judgement—and, as much as possible, have a source that earns your trust.
Be mindful of your use.
Use your vape as a situational supplement and not as your main method of cannabis consumption.