Ras, I don't know...but would think...that you realize that weed, especially good weed, has a very pungent odor. Personally, I have lost count of the number of times I have approached a vehicle on a traffic stop and smelled weed the instant the window went down. Sometimes it's because they've been smoking it, and sometimes it's just because it's there. But I've never thought I smelled it and not found it. It's like walking into Pizza Hut. You just know what's inside when the door opens.
The pros are moving large quantities in well-sealed packages. They can beat me, but not the dog. The amateurs? Unless they packed it away well, and especially if they've just tossed a bag in the glovebox or console, that bag of traveling herb is easier to smell than a fart in church. Fortunately for most, I'm a "grind it into the dirt" type if it's less than an ounce. I've got better things to do than make a living on misdemeanor weed. Same way I let 'em pour it out on open containers. Absent more serious charges that I cannot ignore, I always give them the choice, and so far it's been 100% grind/pour and move on.
Here's a helpful traveling tip: Leave your bag of weed in your overnight bag until you get to Daytona. Don't smoke one for the road, or on the road, and don't roll one for when you get to the beach. Makes it too easy for me. Oh...and vacuum up all the shake out of your floorboards before you hit the road. Too obvious, and automatic PC for a deeper look. In all honesty, I'm not all that interested in you, or your hippie lettuce. But if you blow past me at 90+, and then there's a bag of weed in your car, well...you are what we refer to as "Low Hanging Fruit", so don't blame us if you get picked (on).
This Public Safety Announcement brought to you by those of us who wish you were smarter.