The ability to practice Reiki is possible after initiation directly from a Reiki master. This is something like the empowerment blessings of Tibetan Lamas, or the gifts of the Holy Spirit, which are given only by those who already carry the gift themselves.
I spoke to several Reiki masters before I was happy that I had found someone I connected with well. This process is important: don’t rush it. There are many teachers with many different styles, and you want to find someone you are comfortable with and trust. If you’re still not sure, get a Reiki treatment with them before committing to a course.
The decision to pursue Reiki is one that comes from the heart, like the enigmatic pull of love, rather than something you think out rationally. When you are choosing a teacher, let your heart be your guide.