How do you know he isn't selling meth? OP just assumes it's just weed.I'm just saying, calling the cops on the guy would put him in prison for a very long time. OP can at least go meet the guy to see what he's like and ask him to address the smell of the weed. If he seems dangerous, then I guess call the cops, but most weed dealers aren't hardened violent criminals or anything. It's not like he's selling meth.
You shouldn't be selling drugs to begin with. I wouldn't even hesitate to call 911.