Nov 05, 2009 Nonsense of scenting dogs
The NIH’s caption to this drug dog photo is enough to turn the stomach: "Nice to nose you: Flyer, NIH’s only certified drug-sniffer, serves on the K-9 team along with 10 bomb-sniffers. A dog’s nasal cavities contain over 220 million olfactory receptors; the human version has 5 million." (Image from the NIH’s website).
Overall, I am not very fond of crime-sniffing dogs, as I partially recount in my "Confronting Fido" blog entry.
Dogs are no less fallible than humans. They can be wrong on smell tests. Their handlers possibly are unable to tell when the dog is incorrectly alerting. Being human — and there being a huge percentage of people who are frequently dishonest — there are bound to be police smell-dog handlers who coax their dogs to alert to a smell or lie about an alert that never took place.