With the rise cryptocurrency and the inevitable mining people may be tempted to get involved in, nothing seems more tempting that cloud mining for Bitcoin or Ethereum. The promise is seems to be that you can get a year of Cloudmining Bitcoin and make your money back in two months, and everything after that is profit. The issue that is not mentioned is that mining difficultly always increases. Historically, even in years where bitcoins in didn't appreciate in price, mining difficultly nevertheless increased. Mining difficultly is based on the amount of Bitcoin being minded, and merely will always increase the as the capabilities of mining hardware increases relative to their costs. There is no reason to believe this increase will slow down in the future. Even with the price of Bitcoin being relatively high compared to the difficulty, companies like Hashflare simply raise prices until it's practically assured that whatever you're paying them to mine will always buy more Bitcoin at the moment you pay for it, than will be mined.
Overall you are likely to make money, but less than if you had simply purchase the Bitcoin to begin with. While you could possibly be OK with this arrangement, as you're not losing money, it's not as if it protects you in any way if the price of Bitcoin were to crash, for instance. This is because difficulty depends more on the power of the underlying hardware used for mining. If the price were to lower at this point, it would only if it crashed to the point were mining on otherwise profitable hardware become unprofitable. Much of the mining cost is sunk hardware costs, with an Antminer S9, still one of the most popular new miner sold, costing around $8000 CAD, and it's electricity costs at 1300w and 10c/kwh being around $1100, the price of bitcoin would have to go to below $2000 USD a coin until it was no longer profitable to mine it at current difficulties. When looking at a difficulty chart between early December 2017 and early January 2018, the price of Bitcoin makes no new highs, but when looking at the difficult in that time, it still increases almost 50%. As long as it makes sense to bring new mining hardware online, the difficulty will increase.
Further, even Cloudflare, the most 'reputable' of the cloud miners, will change the terms of service at a whim if it looks like the miner might win out. In the past, they cut the length of already existing contracts from five years to one, when the difficulty hadn't climed fast enough for their liking. They raise prices per hash on new contracts with the price of Bitcoin, even though their costs per hash should be decreasing as better hardware comes available. Plus, there are maintenance fees that they could change at a moment's notice. Seemingly the only way to make real profit mining is to get your own Antminer S9 or similar mining machine. Hoping to make a profit beyond what you would have made with merely buying the coin with cloudmining seems to be a pipedream, and if it is possible, vendors will just raise prices until it's not possible. In theory, I believe both the cloud mining companies and their customers should be able to benefit and make profit past their original investment, but in practice the cloud mining vendor holds all the cards, and due to high demand regardless of what they do, they have no incentive run an honest business and allow their customers to actually make profit. Now, they won't technically run away with your initial investment not pay you out if you cash out, because they don't need to: They're continuously tilting the odds in their favour.