Feedback (ratings and comments) may be removed in the following instances:
There is a violation of the Feedback Abuse policy.
A member is unable to form a legally binding contract at the time the item ended or Feedback was left.
A member provided eBay with an email address that is invalid and could not be contacted at the time of the transaction.
A member mistakenly leaves negative or neutral Feedback intended for another member, informs eBay of the error and has already placed the same Feedback for the correct member.
If a member is suspended by eBay, negative & neutral Feedback left by that member is removed. If a member is suspended within 90 days of registration, all Feedback is removed.
eBay is provided with a valid court order requesting Feedback Removal.
A buyer fails to respond to the Unpaid Item process.
When the communication and comments left by the buyer within the Unpaid Item Dispute Console undermine the integrity of both the Unpaid Item process and the eBay Feedback system.
http://pages.ebay.com/help/policies/feedback-removal.html