Better go for a walk and when you smell some puff puff being puffed puffed, you chase the stinky winky and you offer whoever has it some money in exchange for the weed.
Should work fine, if you spot a group of people just in a sort of hidden area and appearing to be smoking, you can always call them with hand signals, and if they selling they will go to you, no need to get into the hidden place so you keep ur possessions. Always play it safe.
Good luck growmie.