They explained to me that they always brought an advance guy on blind dates. He'd knock on the door and after he was seen by the blind date, he'd leave and let the real blind date take over. Apparently they used this strategy all the time. It got them through the first step, the visual inspection before the door was opened. Once the door was opened the dates were usually too polite to close them again or admit that she was shallow enough to be interested in the advance guy, but not the real date, so they'd continue the date.
No idea how that worked out ultimately.