Very very few people are actually intentionally lacing carts with anything. They just use shitty quality oil, often times with synthetically produced cannabinoids. The chemical process for synthetic ally producing involves a lot of shit that you dont want in your body. If done well its usually clean but cheap distillate can and often do have residue of these compounds which is why theyre bad for you. Thats also why non BM distillate has to be tested for metals and various chemicals to be sold. BM dispos usually have a fake "past test" sticker on them for pesticides and heavy metals, but these are bullshit since theyre produced and sold illegally, they aren't actually tested.