Negative feedback leaves me questioning my business

I am ten months into my business and received my first negative feedback. I actually agree with the criticism from this customer, and I’m embarrassed that she doesn’t feel she got her money’s worth. The product I provided wasn’t the issue, but she felt there wasn’t enough accountability on my part. Now I feel icky. I’m questioning why I started this, and leaves me wondering who else who purchased my product and feels the same disappointment in me. This compounds with having felt imposter syndrome over the last few months. Part of me wants to quit the business and get a “real” job.