If the party harmed by my action was an informed, willing and competent free agent, was my harmful action immoral?

Yeah, another morality question. Many Flutherers seem to consider an immoral action to be one that intentionally causes harm. But what if the one harmed by the action solicited the harm of her own free will, as a competent and informed agent? Am I blameless in the situation if I inflict the harm?

If I sell you something that I know will damage your health, knowing that you’re not aware of those dangers, that’s clearly immoral. But if you buy my product knowing full well that it will shorten your life, am I released from any moral engagement? The physical damage is the same either way.

So is immorality just a matter of intentionally violating someone’s freedom of choice? If they choose the harm, can I provide it with a clear conscience? Or should my actions toward you be governed entirely by my concern for your welfare, regardless of your willingness to be harmed?