One hot summer day 2 FAA inspectors were renting our 172RG. After the one hour preflight, thay taxied out for takeoff. I hear over the radio "Cessna is aborting takeoff" and they pull off the runway. They taxi back and do the same thing. So they taxi back again, wait a long time then take off. A few hours later they came back and I asked why the two rejects. They said the takeoff roll seemed long so they rejected and tried again. Still seemed long so they rejected and then looked up the numbers in the POH and it turned our to be about right. So the third time they took off. They said they would have grounded the plane if it hadn't roughly met the POH numbers. I guess they weren't familiar with the 172RG's nickname of "Guttless".