Answer by David Throop:
The qualities of a good freelance writer is the same with any freelance position, from writing to photography, acting and music.
It requires a person of patience, perseverance, a comfortable dose of delusion and flexibility.
Patience to work with many types of clients. It is a service position, one that deals with all types of client-types, from demanding to hand's-off and everyone in-between.
Perseverance to keep at it even when it seems like its more difficult than necessary.
Comfortable Dose of Delusion to believe in yourself when it appears the odds are stacked against you and the work you're trying to do. You will most often struggle financially, so having the confidence of delusion is a healthy coping mechanism.
Flexibility because you may be writing an article for one client, a blog post from an opposite perspective for another, a white paper for a business and an email auto-responder for another all with the same deadlines.