Us dogs are pretty good at checking other dogs out. We stiff the backend and we can tell a lot about where the other dog has been, what he's been eating/drinking, how healthy he/she is, and what they've been up to.
As a human, don't you sometimes wish you could get to know people better the same way? Well, maybe just as easily anyway. 'Cause as humans I would expect some or a few of the people you work with, that live down the street and that you may encounter in your days have something to hide.
Wouldn't it be nice if you could find out info on them quickly and easily. Some folks do this by doing a Background Check on the person they want to know more about. And lots of employers do a Criminal Background Check on the individuals they are looking to hire. Doing a Criminal Check can help them make more informed hiring decisions I would expect.
But I still say us pups have the right idea...sniffing butts can tell you so much about another dog. That's why it's the first thing we do when we greet a new pup! Don't you think that humans would be able to get along better with other humans if they followed our lead?