Here's a compilation of stuff I've mentally noted down from playing or watching other people play. It should help you.

I'll attempt to update this guide if I discover any new tips.

- Try to cross-reference appearances from the data folder. Doppelgangers can alter the photos in their IDs and Entry requests to match their in-person appearance.

- Make sure you call on EVERY person, as sometimes they might already be in the apartment. Doppelgangers may also carry documents that their roommate claims are in the apartment.

- Ask the person why they're not on the list, even if they are. Most people and doppelgangers will call BS, whilst some doppelgangers will make up a lie, despite being on the list.

- Doppelgangers cannot answer phones.

- In the campaign mode, if you let in a doppelganger, deny anyone trying to get into that apartment to reduce casualties. It is worth noting that they have a chance to be killed out on the streets, but it's not a guarantee.

- Perfect doppelgangers can appear, but only after you let the real person in.

Make sure to like the guide and give me your steam points if this helped you in any way.