I'm considering working in writing. I'd like to save myself some time in case I'm not up for the job. How do I go about evaluating myself as a professional writer? I was going to ask for a peer review of some samples to do the task of evaluation but I saw that peer review of written material is considered off-topic here. So, I have to evaluate myself and don't know how.
You evaluate yourself as a professional writer by submitting writing to respected publications and seeing if they offer you money for it. The beauty of writing is that there is no other criteria, no other qualification you need to possess, no licence you need to obtain. If it is good enough, it will sell. But by the same token, there is no infallible test of whether you will make it or not.
There are, of course, much easier paths to take. You could become a technical writer or a copywriter. Those are much less uncertain paths. But assuming that you mean you want to be a commercial book author, I don't think there is an accurate litmus test.
Developing as a writer takes time. It takes a lot of writing and, equally importantly, lots of attentive reading. The attentive part is different. Writers read differently from other people. We pay attention to how things are written, what works, what doesn't, and why. (See Francine Prose's book Reading Like a Writer.)
Along the way you can submit your work for feedback. Bad feedback does not mean you can't succeed, only that you have not learned enough yet. Nor is bad feedback even a reliable guide to if your work is publishable. Lots of critique groups would rip to shreds works that have sold millions of copies (think Dan Brown or the 50 Shades of Grey author).
But the strongest indication of whether you can succeed may be in your own question. It can be a very long journey to publication, and an even longer one to earning a living at it. It is the Everest of writing careers and most people who try it die on the mountain (or never get past base camp). If you are as ambivalent about it as you seem to be from your question, it is not likely you will have the resolve to get to the top.
From any rational standpoint, writing books is an insane way to try to make a living. The only possible reason for trying is that you are unable to stop yourself. If you are capable of stopping yourself from becoming a writer, do so. We are a ship of fools. Swim if you can.