Especially back in the old days pre-WG pics on the interweb, all you had to go on was the voice of the girl on the phone or worse the voice of the 'maid'. It was a major gamble each time which made it even more nerve wracking, but probably an even bigger rush.
Some would be ok if you said no Ive changed my mind and let you out and you could ask if that was ok to do so on the phone beforehand, but some might not be. Any experiences of doing a runner after the door opens and you see the girl for the first time? Ive had to do this quite a few times in the past. I would usually stand a little back from the door so i could have a good look on the door opening and make my split second decision, although some would hide behind the door as it opened so would have to crane neck round to have a look or would get ensnared inside. I remember one ordering me to get inside rather brusquely and that was enough for me to say no and leg it.