eBay prefers you to view Negative and Neutral Feedback in context with the surrounding Positive Feedback, so that you can get more of a whole picture of a Buyer or Seller's activities.
But here is how to filter just Negative and Neutral Feedbacks the old fashioned way:
Click on the feedback page of the user whose feedback you are interested in. Now scroll down to the bottom of the feedbacks showing and you'll see radio buttons asking how many feedbacks do you want to view per page. The default is 25. Change that to 200 (the max). Now once you have your first 200 feedbacks showing, go to the Windows toolbar at the top of your page and click "Edit". You'll get a drop-down from which you can select "Find (on this Page)". Now you'll see a pop-up box where you enter what it is you want to find. Enter "complaint" and then hit the Find Now button. Each time you hit Find Now, it will take you directly to the next mention of the word complaint. In eBay feedback, all negatives are flagged by a Big Red Complaint at the beginning of the feedback. If you want to read the Neutrals, do the same thing, but enter the word "Neutral" in place of "Complaint". When you are finished looking through the first 200 feedbacks, you can page to go on to the next page of feedback and continue this process until you've scanned the user's entire feedback history.
By the way, don't use my "quote marks" when entering your fields.