You can take a look at the guide from this link. https://itch.io/blog/800154/secret-user-guide
Most probably, hitman comes because your hunger, thirst and mental health values are low. You better keep these stats high before going to sleep.
In answer to your question, let me write down the possibilities of hitman's appearance.
Chance of a Hitman Visiting Your Home:
Ordinary: 5% chance
Low thirst: 10% chance
Low hunger: 10% chance
Low mental health: 10% chance
Open window: 100% chance
Closed Vpn: 100% chance
Virus scan not performed: 100% chance
Incorrect request: 100% chance
Extra- The window lock might break: 5% chance
Extra- The hitman might introduce himself as a delivery person: 5% chance