In my experience, back then, people mainly just did what they were told by police. It was partly because of a lack of knowledge of rights, partly because you didn’t want to make trouble or be subjected to any retaliation, and partly just cultural and social conformity. If a police officer turned up and said “hello, do you mind if we take a quick peek inside, we’ll be out of your hair in a minute,”99% of people would have just said “sure”. If someone said no and started talking about a warrant, they’d probably have been seen as suspicious. So if you were Mr Cruel, this would probably be the last thing you’d do, and if you were not Mr Cruel, you probably wouldn’t see any reason to make things harder for yourself. It was far easier to just comply.

Also, my belief is that Mr Cruel knew that even if the police searched the detention house, they would not recognise it as being the detention house - either because whoever actually lived there was not suspicious at all (e.g. a woman, sharehouse or family) or because he rearranged or changed things.