How can you tell if someone is Stealing Electricity?
I have heard magnets behind the meter in the old days, by passing the meter base and so on.
From you or the utility company?
Their hair is standing straight up? 
“Big Bad Wolf” ??
Theft of service is not taken lightly in most municipalities or Utility disricts. Various ways of turning the meter upside down or running a jumper wire. Just make a complaint and the utility company can verify the condition or make an audit to confirm the currect setup and look at prior utility usage to get a comparison.
Randy