so far, I only buy on ebay, i have 63, all positive, which prolly mean I bought like 200 things in the past 5 years. I avoided getting negative once, I didn't have a CC for an auction I won, and I missed that in the fine print in the header he only took cc's. I apologized and didn't get feedback.
Back in the good olde days I left neg feedback once, one guy was cashing out his reputation and selling things he had no intention of shipping to the buyer, I lost 30 bucks, in 2 weeks, he racked up like 9 negatives. This was before they required the seller to put down a CC.