you would only be able to catch him based on his game. If slot 1 is not playing like slot 1 the following day you can consider him possibly be guised into. granted you need a decent understanding of who that person is and how he is likely to play.
sometimes you can ask everyone to out a guise code day 1. and then ask him what the guise code is day 2 to check that specific slot.
i forgot to mention an important mechanic that is unique. if mafia uses janitor and disguiser on the same person and guiser is lynched, janitored role is revealed.
also guiser visit is a secondary role, so if guiser chooses to visit a person who mafia is not killing it will show guiser visiting someone else aka can look like a drunk visiting someone and he can then CC drunk if tracker was on guiser.
ALSO mimic mechanic shows mimic visiting the player, and visiting himself on a tracker report so "mimic has visited player1, mimic has visited mimic" would be the report shown to tracker.
Guise test is used to check if the player1 is still player1 and not mafia guiser that took on his identity.
Imagine last game Jordan guised into Barry. At day start we would see that Jordan the town Mason Is dead. So we would know that Jordan guised into mason.
If Jordan guised into veronica or Vince it would show that vanilla town Jordan is dead. So we could determine that veronica or Vince is not playing like veronica or Vince and it's likely Jordan who is guised into them.
On EM people at day 1 would leave a guise test codes sometimes:
I _m h _c__nes
And when asked what my code is next day I would reveal it. I am the fucking best. Then you need to think if they code makes sense or not. So mafia can crack it but it's not the only way to catch guiser.