They were probably on the shroomery where this guy was ranting about impure DMT and he's an expert because he had a "QP" in a mason jar (Half of a pint jar full. Looked like maybe an ounce, that's a lot of DMT but yeah the guy is full of it. Nothing works the way he says)
He was going on about someone's DMT being less than 75% pure because of the presence of tan polymers doing a simple STB MHRB extraction. He couldn't provide a source for the contamination only that it was dirty and would cause brain damage, yada etc... Thank the Creator for the Nexus!
TLDR the Nexus is a wonderful place to learn about DMT, I cannot attest to other sources where drug dealer's opinions are held in regard.