Dan Marino is my favorite football player of all time. I've gotten his autograph in person dozens of times, literally all over the country from San Diego to Newark to Houston to Cincinnati to Dallas to Pittsburgh. Some I've sold, some are in my personal collection, and the rest are for sale on AutographsForSale.com.
The first eight Marino autographs shown below were all obtained in person by me between 1995 and 2005, mostly at celebrity golf tournaments but also at the Dolphins team hotel and at the airport. None were obtained at sit down signings. There are some common characteristics, but as a whole, they have as many differences as similarities. It is my contention that Marino's autograph varies far too much for ANY third party authentication company to do more than guess. And guess they do. At the very bottom is a PSA/DNA "authenticated" Dan Marino autograph that is almost certainly fake. Yet another reason why PSA/DNA and third party authenticators can't be trusted under any circumstances.