The vendor who sells many different things seems to be at least a bit less culpable than the provider who sells just their thing while lying about certain effects of it. Yes, we can examine how we got into this situation where doctors take drug advice from the people who make the drugs but the people who lied for profit deserve the lion's share of the criticism.
In practice, even many of the general public knew that what the vendor was selling was addictive and dangerous -- there are some reports even in this thread. So it's hard for the vendor to claim ignorance, even more so when often they also stood to profit from the lie (repeat customers).