I believe the police in this case. Why would people break into a Rolex store and not steal expensive watches that are close to impossible to track.
Beyond that, there are other holes in the story like how exactly the police managed to come up with the $2.4M figure apparently without any collaboration from the store itself, or what motive Rolex SA would have to lie about losing $2.4M in merchandise.
But as always, people are primed to believe that the police _must_ be telling the truth somehow, even in a post about a whistleblower laying out years of lies and deception on their part.
I 100% believe that there were no watches on display. Why would the store spokesperson lie?
But I'm wondering about your scenario: if the watches had been stolen, how would it make sense for the store to lie about this? Rolex, a member of a conspiracy against the police?