Fake sport collector cards are probably the most popular fakes on Internet. Sold for thousands of dollars or even more, they can be fabricated in any dorm room. Along with them, signed soccer, hockey or football jerseys has raised the total fraud over the years to over 200 million dollars.
Scammers successfully sell their “products” after they forge the authenticity certificates as well, which lead the victims to believe that what they buy is real.
Another variation of the scam is represented by online auctions for items supposedly used by famous actors at certain filming locations, such as pieces of hair, cigarette butts, pens, etc. The scammers, who reside in the city where the film was shot, claim they picked up the item after the famous actor used it (eg. you could be sold an empty soda can, which Jack Nicholson, apparently, drank out of on the set).
How to avoid: it is a tough one. As difficult as it is, always take your time to research the source of the item. Just because the seller says something, that doesn’t have to be true. Look as his feedback received from previous sales and ask him for a proof that the item is really what he says it is.