These exchanges end sanctioned market manipulation known as HFT - High Frequency Trading, which is simply spoofing and paint-taping writ large.

They use that 'liquidity' to puff up markets and move them up and down with a fraction of the money that is actually up for trade. In short it's fraud. Most of the orderbook of these exchanges has zero intention of ever being hit as they disappear before you can hit the bid/ask.

Their computers are faster than yours.

The end to this is making them have stake in their position. BitShares forces listing fees on them. BarterDEX requires you have the coins and must wait in a time-locked contract for the other side of the trade to confirm and post a fee to do so as collateral.

This ends 90% of the problem. Then since neither are trading off-blockchain there isn't the bullshit of moving from coin to coin without ever confirming the change in ownership. The exchanges are running fractional reserve systems and settling on the blockchain at regular intervals.. say every hour or two, a lifetime in the crypto-markets where a coin can move 10-20% and leave the exchange short of funds.

Liquidity meet trap.

Read this post of mine from this summer on spoofing:
https://tomluongo.me/2017/08/07/will-cryptos-end-spoofing-or-enable-it/