Like ryhog said, the transactions are mostly made online. If you buy a ticket that is emailable, you get it by email. If someone is selling a physical ticket, you have to either wait for regular mail, or pick it up at a brick and mortar location.
It's not a new service, and they're pretty legit. I don't know what the likelihood is of getting tickets below face value. But you can look and follow online to see how they look - people control the price and they often do lower the asking as the event date approaches.
I've sold emailable tickets and I've bought tickets for sports events.
