If you come to me with 2 juice boxes and offer me one while drinking from one of them... I would fully expect to get to non-drank-from one instead the one you just sipped on.
Either way I'd probably say no thanks, I'm good. But if I were to accept it, sealed reduces suspicion by 20% because tampering is still possible. Purchased reduces suspicion by 97.3%, but randos don't randomly buy things for other randos, so I would be looking for the person filming the tiktok prank or brace myself for the evangelizing that comes with the free drink.