I’ve never actually played, so this might be standard practice anyway, but I think this would be a great time to have the DM roll privately for each player and not tell them if they passed or failed. If the players only know what their character saw (and not if they pass or fail the check, or even get an idea based on the roll) then metagaming is impossible. This could produce a situation where it’s just a dog but the paladin thinks they saw a monster because they failed the roll, or it could be the other way around.
Doing it with DM-only rolls ensures the players have to actually figure out what they saw rather than knowing based on what they rolled or if they passed.
As I said, this could be standard practice, I have no idea. But I hope it is.
The player could describe what they saw, but nobody except the GM knows if it’s true.
It’s equally plausible that the paladin failed the check and saw a monster when there was only a dog, or that they passed the check and saw a monster because there was in fact a monster. Their argument to the party would be the same in either case: “that’s no dog, it’s a
space stationmonster”.The party then must question who saw the correct thing. Did the paladin actually see something everyone else missed? Or are they just seeing things? My point was that the players should not immediately be able to discern the truth. I find that this kind of uncertainty breeds intrigue!