Does the complex have CCTV? If so, might a screen showing people entering the complex embarrass paying guests? Especially with a pull through on the screen advising that footage is shared with police as required.
Of course intercom entry would prevent people just wandering into the complex. This is another issue that affects all residents.
Have you talked to the resident and asked if they are running a business? If the confirm they are then you can ask how they ensure the security of other residents in ensuring they know who they’ve allowed to enter the building and that customers leave once they’ve concluded their business.
If the business does involve intimate matters then there is also the potential for hazardous waste. How is this being disposed of?