You cannot trade any (crypto)currencies directly.
Ok, this is bad, this means that projects like Blocknet are far superior, because there you can trade cryptos directly.
* SmartCoins aka Market-Pegged Assets - these are loosely coupled to the external currency they represent, see Question 9
SmartCoins in BitShares rely on an external "price feed". The owner or issuer of a SmartCoin can specify a number of trusted users who are allowed to publish the external price of the token against its underlying asset. Typically, SmartCoins are owned by the committee, and the price feed is published by the witnesses (who also sign the blocks).
So ti is centralised and requires you to trust a party? So it is not trustless, not decentrilised and not censorship resistant, correct? These parties can censor and alter data, correct?