Being prudent with other people's money is nowhere near equivalent to promising 100% reliability.
Who is being imprudent? The company who owns the satellite is or should be fully aware of the risks involved. The company who build the rocket has an obligation to disclose any known or reasonably foreseeable risks. As long as those two things happen and both parties are ok with the risk involved with it then there is no problem. Nobody is being taken advantage of here. One side pays the other a risk adjusted fee for launch services with the full understanding that the launch may fail. If the satellite owner isn't comfortable with the level of risk being taken then they shouldn't sign the contract.
Now if unreasonable promises were made or the rocket maker lied about what they were doing then that is why we have a court system.