I have witnessed many unexplained phenomena in my lifetime. I dare say some witnessed me. You may not believe it to be so, but most prayers are also exercises in black magic. 'Magick' is essentially the keen focus of one's will on a given situation. It has been theorized that the human mind can and does influence physical reality. This is a theory, however. If it is true then the focus of one's will could be fruitful. I well can and do believe that Will influences reality.
Results tend to vary and would depend on the wishes and the level of faith in the "magic" one practices. If a person believes enough then they can give their magic credit for anything that happens if they so choose. There's no difference between true believers practicing black magic and people of other religions praying to their god/gods and crediting those prayers for doing what they want them to do.
The understanding of what a wish is and from whence it came is pivotal. Many practitioners believe that their wish originates in what is called the mind and then proceed to use the mind to conjure up some wish fulfillment. In this case, as always, a huge consortium of causes besides the mind contributes to the outcome, and a spell may not achieve the desired result.
However, the general nature of a "true wish" that is, one that is generated from a state much deeper than the cognitive ego is closer to the source of the Will of all creation. In those instances, the Will and wish are better aligned and the outcome headier. Not their wishes, per se, at least not generally, but they may find a higher incidence of things occurring which they have done spell-work toward. Whether the magic is considered black, white, green, or purple doesn't matter, though - only the innate ability and trained skill of the practitioner.
If the individual in question had properly aligned themself with a beneficial & benevolent powerful deity or a pantheon of deities in addition to utilizing the appropriate items during appropriate times, then absolutely nothing bad shall happen to the individual. I can testify from my own personal experiences & practices, especially when doing rituals/spells involving *Blight/Destruction* or *Death/Illness* for the purpose of revenge...
It depends on the person who is practicing it. To control energies you need a great deal of self-reliance and spirituality. The paranormal activities in an environment are not easily identified by an ordinary person. The first step for anyone to understand magic is looking into the inner self. If you can generate a force with the thoughts you have, then you reach a state where the mind can create its own powers.
Em Hotep - Patrick Gaffiero