I disagree with the proposed fix. As an English major software engineer, I would treat that as a run-on sentence. First, you should clearly ask yourself if the sentence is necessary before looking for a fix. If you find that the sentence is useful then break it into two sentences, use active verbs, and make sure your logic is clear.

The original sentence begins with the premise: my writing is not perfect. It ends with: I think highly of myself. Self-esteem and writing quality may be unrelated.

"My writing is hardly perfect. However, I write better than a typical salesperson."

I love the epiphany by the author of the comment. Communications is a HUGE factor in sales. Clear, effective writing will amplify your business overnight.