If you're that worried don't do it. It's the same thing as doing a couple pulls on the road and actually safer since you are on a dyno. Your car is improperly strapped then you can sue the company or car shop, because it is their negligence that caused it. You can get a compression test etc to make sure your car is up to par. I don't know what you are so afraid of. If your tuner is good and you are going to a good shop and your car is running strong then I see it no different as doing a couple pulls on the road. In actuality getting a proper tune makes your car run better and more reliable in the long run. Stop being a little baby and go get your car dyno'd and post the video on youtube if it falls off so I can laugh at you.