No one has free electricity.
If you think you have free electricity, check your contract. There is always a fair-use statement.
A S9 can easily reach 10$ a day, so for 2, that is 600$ a month. It can be easily spotted on an energy bill.
With the noise they make, they can easily be found in a building.
They are connecting electricity cable in "stealth" mode to the network. So here the contract is not needed

But need to hide this connection really good in case of Inspector's visit.
You're probably right, the electricity he is using for free is not actually free. It's either stolen or someone else is paying for it (technically can also be called as stolen). This would really make this profitable, although it would be risky on his part. Well, the law on risk demands that the higher the risk the higher the potential return. The risk involved here is getting convicted for stealing electricity.