ETH is too young for giving any big trust in. That's why this can happen even if this seller was only one and unic personn. Better to this happens now than later. And i'm not surprise of this situation. But ETH will probably grow up again. More people will be interest in, less this kind of effect could happen. But the bubble in what ETH get in, was too huge compare to the number of actors in this crypto. We should not juge too fast. Time will speaks.