I suggest researching it. My personal first thing is hardware, I would verify hardware as this get's rid of a LOT of the crap sites. They just don't have any proof of hardware.
Next I suggest looking at history. Read about it and other peoples experiences on the board.
And third make sure they don't use things that are too good to be true. This sounds stupid but it honestly is a good idea. If it say's like "lifetime", "forever", etc. Chances are it's to good to be true no miner lasts forever. They have a timeline depending on efficiency, and charges.
But research these and you can cut down a lot. I personally don't push people into investment as I have said many time's I make 0 no matter what you choose on cloud mining. I just push for research before investing I think for most you will end up with just a few sites after above. But feel free to add other ways to investigate if you have them I would love to have more good ideas.