If you are selling drugs openly on a street corner in an area known for drug dealing, your probability of being arrested for drugs is far higher than a white who doesn’t traffic openly on the street.
Many trafficking charges are pled down to possession so it appears that the person was simply a user, not a dealer.
White marijuana users and dealers are much more secretive about their participation in illegal drug use of all kinds.
Organized black drug gangs in major cities station street dealers in a specific spot. These guys sell small quantities—single joints and small packets (sometimes match boxes) of loose marijuana. The dealer keeps a limited quantity of product on his person. When he has sold that quantity to various customers a runner delivers more product to him and collects his cash. There are many clever variations on this technique but it limits the dealer's criminal liability.