While Perception checks are technically just a type of skill check in OSR+, they require more finesse to run successfully than other skill checks in the game. This is because a PC's perception is central to how they interface with the fiction, so players will frequently use the check in lieu of actually investigating a scene. But Perception checks are not a substitute for interrogating the fiction, so we need ways to mitigate this behavior and teach players to engage in the conversation.
Investigation vs. Button-Pushing
Players should not go into a room and ask "Can I roll a Perception check to look for clues in this room?" because a skill check gets triggered by something the PC does, not something the player declares.
When a player leads with a Perception check, ask them what they are looking for, and how they're doing it.
The key to resolving a Perception check is recognizing that it can only ever surface a clue about the thing the PC is investigating. If the PC is trying to determine if an NPC is lying and they ask about the NPC's body language, an opposed Perception check might reveal that the NPC is sweaty and fidgeting.