I am basically going to give you the same advice you see here.
1. Always buy from a reputable dealer
2. Know that Marino is one of the most faked autographs out there.
3. Always look for either an Upper Deck, PSA/DNA, or Marino hologram.
4. If you want to cover yourself do this:
Ask the seller if he will guarantee it authentic and that it will pass a PSA/DNA test
Then send it to PSA to get the signature autheticated. They are the leaders in the industry and the recognized experts. It will cost you a few bucks, but worth it.
If it passes they will put their own stickers on it and you are set forever. If it does not pass their insepection then you can go back to the guarantee from the buyer and either get your money back, or file a complaint with Ebay. PSA also has a "quick opinion" program where they will look at a picture of the signature and tell you if they think it is real or not. Small fee involved.
In the end I think it is important for everyone to know that when you buy on EBay you are taking a risk. That risk goes down when you look for holograms and certifications from reputable dealers like Mounted Memories, Upper Deck, PSA, etc. If you buy from someone who gives their own "Certificate of Authenticity" then it is real worthless as anyone can make those up. We all like to find good buys on memorabilia but if you want to know you have real stuff, then spend the extra money on the certifed items. Also remember that the ultimate value is in the eyes of the owner. If you believe an item is real and you are happy, then that is cool.
My final opinion on this specific autograph is that it is a bad real autograph. Meaning, that the player didn't do a good job of signing it. The pen strokes, lines etc. look like Marino's, but it looks like he crammed it into a small area and maybe this was later in the signing when he was tired and just wanted to get done. The result is a bad signature. I caution it could also be a fake and that is why it is bad. Just my thoughts.