Well I don't think ponzi is the right term here. A cloud miner could not be mining and not operate a ponzi.
A ponzi is usually defined as something where new client money get's used to pay returns to existing clients.
Which is precisely what these mining ponzi's do. Often times you can even trace the payments from purchase to "dividend"'.
What makes a cloud mining ponzi different from many traditional ponzi's, is
1) there is no risk of a bank run.You can not get your money out because these contracts are non refundable. You may be able to trade them with other users, but the operator doesnt risk a withdrawal rush. (But thats also the case for many traditional ponzi's where the investment is locked in for a certain period for the same reasons. Its just that with mining ponzi's, this sounds like a reasonable thing);
2) Less than 100% ROI can be expected depending on how difficulty evolves, see below:
(most) cloudmining is Ponzi 2.0.
A "fake cloud miner" could be running a scheme where they keep a enough money to pay every single mining contract it has sold. You can estimate the amount of money required to pay out for a mining contract. Usually (if the prices were calcualted correctly) this would be less than the person paid for the contract. So if you just kept their money until their contract closes you won't be operating a ponzi technically. For cloud miners operating in this manner they are exposed to lower than an expected difficulty as they would have to pay out more than they have potentially.
So what happens if difficulty slows down enough that these contracts ought to be profitable? Where is the ponzi going to get the money from ?
What you suggest could only work in theory if investors lose money supposedly due to increasing difficulty instead of theft, but they lose money nonetheless.
So either you lose money because the ponzi collapses, or you lose money because your contracts are unprofitable. There is no chance (on average) to profit.
Of course, in reality its far worse; regardless of difficulty, do ask yourself, why would the operator pay out all or nearly all of what he collected? Considering virtually all these ponzi's are being run anonymously, use coinmixers to hide their tracks etc. What makes anyone think these people are lying about the business model and hiding their identity but will voluntarily pay out nearly 100% of their loot to fulfill their contract?
BTW, there are ways to gamble on difficulty that dont involve ponzi. You can trade B.MINE and B.SELL on havelock. Its a transparent way to let you bet on theoretical (un)profitability of mining. Unlike ponzi 2.0, its actually quite possible to make a profit that way.
