I think the most difficult thing to do is to keep a 100% feedback score on E-bay. The reasons for that being very easy noteable. Some sellers and bidders are just not meant to keep a 100% profile concerning feedback. Me myself tried for a long period of time to keep a 100% feedback profile, but lost it due to a bad seller that had no respect for a regular client that always paid on time, and bought a lot from him. I use this just as an example, but it would prove my point somewhat.

I bought a few watches from a seller, to be exact 3. I paid for them on the same day. After 2 weeks I received 2 of them. After enquiring where the 3rd watch was, the seller comes back to me with a rude attack of personal kind. This forced me to make Paypal claim. The seller, out of revenge immediately rates me negative, although I have paid for this item in full, and should have had a +pos  feedback from him to start with. But this seller was of the sly type and kept his options open just in case he had to revenge!!

This also forced me to retaliate, and it was the sweetest thing for me ever, to also rate him negative, and I do not even feel bad about the negative rating I received from him. He in fact is a seller,and more bidders would in future think twice before buying from him, if they had a look at his ratings, after all, there are many other sellers on E-bay! 

Instead of following the communications route, the seller arranged a negative rating for himself, and also in the process throwing away a lot of money that could have been earned in the future from bidders and myself especially. I call this sellers attitude "the think about now and not tomorrow" attitude!! 

Point : If you can not keep it 100%, it won't be a shame!!...but still, if you can keep it over 90%, it would just look better!!