Phasmophobia

Before beginning, a quick note: Like all ghosts except the Deogen, the Yurei appears randomly. Since there are ~25 ghost types at the time of this writing, this means your chance of encountering a Yurei is less than 5% on any given investigation.

The Yurei is one of the more difficult ghosts to identify. Its three evidence types are ghost orbs, freezing temps, and the DOTS projector. The first two are fairly straightforward, but here are some thoughts on all 3:

Ghost orbs: I would recommend always trying to identify these through the use of a tripoded video camera in the ghost's favorite room (or what you suspect is the ghost's favorite room). Do not attempt to look for ghost orbs before you have a candidate in mind for the favorite room, as this will waste valuable time. To make it easier, shut off any light sources in the room.

Freezing temps: The T1 thermometer is notoriously unreliable as the mercury will fluctuate up and down a few degrees. The game considers temps below 33.6 to be freezing temp evidence. When using T1, I wouldn't consider it conclusive evidence unless you're at 30 or below.

DOTS: It is easy for newbies to fumble this evidence because the ghost does not produce a silhouette 100% of the time when moving through a DOTS field. It is a relatively small chance and the ghost needs to physically be in the field. To increase your chance of positively identifying this, bring multiple DOTS projectors to increase your coverage in the favorite room. Also shut off the lights. You can search this evidence in tandem with ghost orbs because that will also help you identify a goryo, which only appear in DOTS when no humans are nearby. If you are only getting DOTS hits when no one is in the room, that is evidence of a goryo and not a yurei. Or to be more specific, if you get a DOTS hit when a human is in the room, you can rule out the goryo; and a yurei is still possible.

The yurei's special ability is to slam doors and cause a 15% sanity drain on nearby players. This can be difficult to notice because you would need a door to slam, close to a player, and with another player watching the sanity monitor in the van. Just keep an eye out for doors slamming more often than usual, including the exit door. If your exit door is slamming a lot but not locking like it would for a hunt, and your sanity is lower than you anticipate, this is strong evidence of a yurei.

The weakness of the yurei is also another way to identify it. It returns to its favorite room when smudged (incensed) outside of a hunt and will be trapped there for 90 seconds. If you smudge a ghost and immediately notice activity in the favorite room each time, that is strong evidence.

Note: Like all ghosts with ghost orbs, is it possible to confuse a yurei with a mimic. You usually need to rule out other forms of evidence when discovering ghost orbs so the mimic doesn't fool you.