I think, as in most areas of life, simple categorisation is a blunt instrument - 0 feedback means nothing, but the things you were smart enough to consider are more revealing. I would no sooner make a 'rule' on the basis of a generalisation about Ebay history than I would on any other external, simplistic criteria. You have done exactly the right thing - I have been burned and thrilled by Ebay encounters and I can honestly say the amount of feedback had little or nothing to offer in terms of predicting what happened.