They are fakes. From China. Some people do buy these as they are significantly cheaper than LEGO's version, however there are also problems. The quality varies greatly with some figures almost as good as LEGO, while others won't even fit together properly (see the close-up pictures in the auction). Also, the print rubs off of them quite easily. If you are just planning to buy them for a child who doesn't care about quality they are good alternatives. However they are not suitable for collectors. Also, consider the implications of ripping off both LEGO and Marvel/DC Comic licenses.
They are knockoffs, I have ordered superhero minifigs, as well as bulk minifigs, from Ebay and they are definitely fake. That is not to say they were terrible quality(although some were) but you can tell by the way they fit together they knockoffs. The paint, ease of attachment, and sometimes the overall design is a dead giveaway.
Definitely look like knock-offs to me. The plastic just doesn't look quite right, even down to the reflections. I'd be concerned about buying knock-off LEGOs for a child - you have no way of knowing whether the materials used in the construction is safe, and also high risk of bits snapping off. (although that's probably true for LEGO in general).