Istbor
Dances with Gnolls
Last session my (expertise-in-Arcana) character asked to identify a potion. DM: "Why don't you try a sip?" Me: "OK". DM: "You die. No save."
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Well... That seems more of a DM thing. Why my group find potions, and attempts to identify them, I give them a general descriptions, color, thickness, sent. Mostly, potions that provide benefits will vary in their description. Poisons are typically more vile, gross, or not appealing to look at or smell.... most of the time....
While sipping can help them guess at it, an alchemy kit or alchemist is the safest of routes.