Some folks seem to know exactly how eBay, Lego, and the rest of the world works, despite the contrary experiences of others. My ex-wife was like this.
Anyway, it doesn't hurt to keep in mind that for the most part, you are dealing with other PEOPLE in this business. Like eBay CS reps. Case in point:
I spoke with one weeks ago, very distinctive voice (difficult to understand) and personality. Despite being somewhat formal, this person helped in removing a shipping defect from my selling account and told me, at the time, that another could be removed (low "item as described" rating) if I could get confirmation from the buyer that it was entered by mistake - which I suggested, considering that the buyer had left enthusiastic positive feedback.
A while after I got the (friendly and helpful) buyer to reply that it had indeed been an error they weren't aware of, and the item was "perfect in every way", I called back. A different CS rep looked at it and told me the defect would be removed. After two weeks, it wasn't.
So I called again and talked to the original eBay CS rep (in this story) again. Guess what? I was told, quite firmly, that there was no possible way to remove that low rating, because it was tied to the buyer's feedback, blah blah blah... I could tell I was simply being stonewalled. I didn't bother pointing out the conversation from weeks prior, I simply asked for a manager because I did not feel like I was being assisted as a customer. This person attempted to argue with me, quite strongly, for several minutes, professionally, but very stubbornly. I had to ask about four times for a supervisor, was put on hold, then quite a while later, told they were too busy and I could expect a call back. They refused to give me a time frame. I shrugged it off for the time being.
The NEXT morning, I get a call from a supervisor. I was busy at work and told them I didn't have time to talk but could try to call back in about 15 minutes. Paraphrasing, I was told, "I just wanted to quickly let you know that the defect you called about has been removed from your account, and please let us know if there is anything else you need. Thank you for using eBay."
I also told a story earlier in this thread where I dealt with negative feedback left because the buyer decided AFTER their son opened a polybag that it was too small for the price. Despite being told over and over that honest feedback can not be removed, you certainly won't find it on my profile.
Be persistent when you know you are right. Be as polite and professional as possible. Don't assume you know everything, or that everything you are told is correct.
That said, I do agree that eBay is set up to hose the seller when buyers behave poorly in general. But it certainly is not the 100% all or nothing dead to rights swear on my grandmother's grave scenario that some here make it out to be.