It's not really possible for someone to sell bitcoin that they do not have, these same like very false accusations without much to actually back them up. Please provide further evidence to support your point and then I might be a little bit more inclined to believe what you have to say,
Posible if you - Bitcoin exchanger
Possible to sell them but it's not going to last very long, people will soon decide to withdraw them and then there's no actual bitcoin there for them to withdraw. Only way it would work for an extended period is if people never withdrew or enough deposited to cover it.