eBay's feedback system can be a useful tool for determining a seller's reputation, but it is not foolproof. Some buyers may leave negative feedback due to misunderstandings or personal issues, while some sellers may try to manipulate the feedback system by leaving fake positive feedback for themselves or fake negative feedback for their competitors. It's important to use the feedback system as just one factor in determining a seller's trustworthiness and to also do your own due diligence before making a purchase.