Because not all mail is scanned with canine detection and dogs are not infallible, there are many factors that can interfere with how effective a dog is at any given time. Often when mail has been transported and the cargo has been exposed to high heat hot poorly packaged weed will stink to high heaven, enough to alert the postal worker/customs and trigger a more thorough search. @ TheYowie... clearly a lot gets through unmolested, not sure what sort of reassurances you want, if it sketches you out that much maybe order domestic and avoid customs altogether for peace of mind.