John, you have very few jobs with feedback left. Why are you closing those jobs instead of having the client do it so they are forced to leave feedback?
Also, for the jobs you do have feedback on, a number of them have less than stellar feedback aside from the most recent fiasco, why do you think those clients were less than satisfied?
The way to fix your JSS is by picking jobs you know you can deliver 100% and managing client expectations. You need to figure out what went wrong on those other jobs.
Also, be careful that you are not taking jobs that are doing someone's homework. "Economics essay" and its description sound pretty much like you did someone's homework, which is not only a TOS violation but academic fraud. Just giving you a heads up what that looks like, and that it casts doubt on your profile.
As far as vetting clients, make sure to look at how the clients have been rated as well as the feedback they have left for previous freelancers. This will give you an idea what it's like to work with them. If they consistently leave poor feedback and are hard to satisfy, then you know you should steer clear.