Use Facebook insight.

There is a feature in facebook that you can use to identify your potential customer and i'm revealing you a simple trick.

Choose a 'public figure' of your niche: as an example if you are a personal trainer you can choose a very known name, then go to facebook insight, in the business manager, and put the name of him.

If it's very well known, probably he has a fan page or something, so Facebook will display you the identikit of the people interested.

They go VERY IN DEEP: you can see how much they earn, what is the average family, where they live etc

Write down these datas.

You can use it further also for paid ads.