The purity of the CO2 isn't really a question. There are a limited number of ways to make liquid carbonic and they all result in a very pure product. I suspect if you went into the back room of a paintball store, there would be a couple 50# welding/beverage tanks.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk