City parking officer will use marker to mark your tire (either on the side or the surface of the tire). They use this marking technique to tarck how lonmg you have been park on the street. When you park your car on a street parking that has time limit, make sure you wipe off marker on your tire, and move the car to a different parking spot. If there still marker left on your tire, it may cause confusion that you car has been parked there more than the time limit even though it is not.
Also, you can dispute the ticket by go to the city hall, and tell them you want to dispute the ticket, and they will set a court day for you to attend. At the same, they will notify the city parking officer who issued the ticket to attend the same court. Judge will listen to both sides, and make the final decision. If either one side absent from the court day, and final court decision will be in favor of the side who had attended the court.
Yes, this does happen. You can file complain to Ottawa city council. Or there may be a phone number to call on the time meter. I think if they get more than one faulty meter, u don't get any fine.