Dogs have an amazing sense of smell and can be trained to hit on a very specific odor. Properly trained Bed Bug dogs will correctly identify live bed bugs only and will ignore dead bugs and their fecal material. A Bed Bug dog would be most useful in hotels, theaters, and churches where people come and go. The dog can quickly determine if there are Bed Bugs present.
In the home, I just ask the person if they are being bitten by Bed Bugs. They can usually tell me yes or no and I inspect to verify. No dog required.