I rented an aerator for my lawn. The tech guy in the yard was very helpful in teaching me how to use it. When I got home and used it, the aerator kept on stalling on me. What a 2 hour job turned out to be 4 hours. When I brought it back the next business day and told them about my difficulties, the guy inside at the service counter, said that if I have a bumpy lawn, it will trigger the oil sensor in the aerator to shut off. Thanks for not telling me at the beginning of the rental. Who has a perfectly smooth lawn? I probably won't rent anything mechanical from them again.