I think it depends on what state/country you're in. Here in Oregon they have some pretty strict testing requirements. Everything sold in a dispensary has to be accompanied by passing test results. Oregon also has some pretty strict labeling requirements for nutrients as well which is why there are hundreds of products on a Stop Sale list. Most are cannabis specific products that don't list what's in them and get caught.
"The Oregon Health Authority (OHA) is responsible for
Cannabis testing rules that apply to both the medical and retail market. Any marijuana or marijuana product intended to be sold at a dispensary or retail shop must have been sampled and tested according to the testing rules.
Any laboratory that tests marijuana items must be accredited by
ORELAP and licensed by
OLCC. Only
accredited and licensed laboratories may sample and test marijuana items.
All marijuana items transferred or sold to a dispensary or retail shop must be accompanied by documentation of passing test results."
www.oregon.gov