Reputable exchanges don't keep trading assets they suspect are under 51% DDoS attacks. Coinbase shuts down assets at the slightest inclining of an attack. It pisses off their customers to no end, but guess what, nobody loses hundreds of thousands of dollars
This doesn't make them scammers
Yes it does....
They are selling an asset to someone and the buyer will never be able to take possession of said asset because the seller is refusing to deliver
Who are they more specifically?
They (the exchange) are not selling anything (well, unless proved otherwise). Both buyers and sellers are clients of the exchange (read, traders), and it is them selling and buying everything, not the exchange itself. Simple, isn't it? Does that make them (the exchange) scammers now provided LiveCoin had warned their clients about the state of the asset as in "trashy" (read, you are on your own)?