Even if you provide the best service and product possible, you will still get people that will leave a negative. IMO... I've worked in customer service (even outside of ebay) for YEARS. And some people are just impossible to please.
Yes sir, you got free shipping. How then did you leave me 3 out 4 for shipping charges?
The complete step-by-step guide to get back to selling today!
I think part of it is that we are programmed to just not rate anything other than "average", which would be 3. Not quite perfect (5). But not terrible (1).
Of course, I just got hit by a moron that nailed me with 1's all the way across in my other store because she was unhappy with only 1 aspect of the purchase. And she purchased 5 items. Had 100% fb and 4.9 & 5.0 across the board. Even hit my shipping. She received free shipping.