Without a proof of hardware and/or solvency it's not possible to tell if a cloud mining service is legit.
All you can do is make a bet on it.
As said in another thread, I do think proof of hardware is a bit of a red herring. You can't tell anything from photos of hardware, if that's what you're looking for. Someone could easily photoshop that. I would put more stock in lunamine because they seem to be honest and upfront about everything, including information you might not like, such as fees and length of mining contract.
Other cloud sites have their terms but just simply do the math and you can see it's too good to be true...so then it usually is.