The problem is that the guy who sells is also usually more than an occasional user, at least from what I have seen. He tends to sample his wares and forgets little things like closing the garage door so neighbors don’t see his garden or staggering the buyers so it doesn’t look like the drive up window at McDonalds. He also has access to the tougher stuff that Officer Friendly is really interested. Plus he has to associate with more unsavory characters in order to get the stuff.
Personally, I don’t want my kid visiting Cheech’s place on the off chance that his connection decides to drop by and collect on a debt that the stoner forgot to pay. Or on the chance that the boys in blue want to make a bust to show how tough on drugs they are.