pardon my ignorance and the somewhat unrelated question: what kind of screening do services such as AirBnb do to both parts of the transactions? Or ebay? Shoul

pardon my ignorance and the somewhat unrelated question: what kind of screening do services such as AirBnb do to both parts of the transactions? Or ebay? Shouldn't a well-designed "reputation" system actually mitigate the need for an individual screening?