First, don't repeat keywords over and over when they don't make sense. Second, much like becoming a good rapper in order to become a good writer is to have a large arsenal of words to use that have the same meaning. With this, you can avoid keyword stuffing. While this may be a good approach on how to avoid keyword stuffing, you want to ensure that you still mention your primary keywords and sprinkle them throughout your content. This doesn't mean say it over, over, and over again and make your content hard to understand or make sense.
If you buy or even write your own content, then you should stop every once in a while hold CTRL, and press F. Then type in your keywords and check if you are overdoing it! When it's lit up if you see that you mentioned it over and over, go back and replace those words with some different variations. After you are finished it's always a good idea to go back through and read your article and see if everything is up to par. By following these steps on how to avoid keyword stuffing, your content will read better, rank better, and probably be much appreciated by the person reading it.