it is data that they show not information, so it is raw and can be interpreted anyways you like. as for trust, there isn't much they could fake because it is the data that they fetch from the exchanges and then show it on their site.
i wouldn't say they are or even can manipulate the market because they simply have no power. but they certainly can mislead people. for example two biggest things they are doing is the "dominance" factor which is meaningless and "ranking" altcoins and the concept of "top coins" which is just as meaningless.