There are few ways to know, though,  these days it becoming complicated.
What I usually do when I was interested in cloud mining then is to always run a deep background search on it, about the company and where it is located.
This is very essential because at the process, you will surely discover something which might make you want to use it or not.
Apart from running a background check on it, also try to read recent reviews because you would see people who might not like the way the company runs and why.
Also make sure these reviews are from genuine people who might have used it. Because sometimes, some companies buys reviews just to look good.