if they’re int/dex/str, I make them roll a wisdom check to see if they do something impossibly stupid.
if they’re wis or cha, they roll deception against themselves with disadvantage. It’s excellent seeing a character literally deceive themselves into doing something dumb.
Ok, so, the trick is to make sure the NPC’s are the same way. That’ll really confuse the players.
Person jumps off a roof and splats in front of the party
player: “why did that happen?”
dm: “They had just purchased boots of flying from an untrustworthy source and figured this was the best way of testing them.”