Not every cloud mining site is a ponzi.Some are HYIP'S and some are sheer scams.There are a few trusted cloud mines though like the one here on the forum http://www.cloudmining.website/.There sig campaigns is been running since Jan 2015 so I'm guessing they're legit and safe to invest.More information could be found out on their official thread.
Lol, great new criteria for establishing legitimacy of a cloud miner: how long has their sig campaign been running?
A way of analyzing cloud miners and their ponzi potential is outlined in this old thread which you might find useful. Funnily enough, its credibility is questioned mainly by the shills for that thing you describe as "trusted".
https://bitcointalk.org/index.php?topic=878387.0