"Log Caravan time for free"

How can that be legit? Are you acting as a required crewmember but not getting paid for it? Are you not a required crewmember but just riding along logging the time? There are ways to make some of this "legit" in the FAA's eyes, but many professional pilots take a dim view of it. Especially when it's used as a marketing gimmick to get people to attend a flight school.