Amateur photographers mainly take photographs as a hobby, regardless of whether those photos are taken on a smartphone or a DSLR. Likely, they will have begun on a smartphone or an old camera and progressed to a more a semi professional camera setup from there.
An enthusiast photographer has been an amateur for some time and has learned the ins and outs of composure, all the various settings and so on. An enthusiast may even be at the same level as a professional photographer but, for whatever reason, does not get paid. Enthusiasts likely have a considerable amount of equipment but probably not as much as professional photographers.
Professionals photographers get paid in exchange for the work they do. Many, are incredibly passionate about their work and photography, having built their hobby into a business. A small few see it only as a business and a means to make a living. These are likely to have skipped the hobby bit and gone straight into opening a business after completing a photography course. Look for professional photographers who have a collection of their own personal work they’re proud to show off and talk about.
Based on personal anecdotal evidence