You'd be surprised. The reason that spot works so well is because it exploits something we all use during the game: Pattern Recognition. That's how we're able to instantly discern between a dead body, and a player lying prone. We get used to seeing patterns and associate them with other things.

In that shop, if anyone has been through it any number of times, they begin to see the Mannequins, and they learn not to react to them, after all, why would they? So a player standing up in that shop in the right place is going to be first associated with a mannequin until they see something that suggests otherwise (red name tag, maybe some movement), or unless they're deliberately looking for someone amongst the mannequins.

In almost every instance, it's the red name tag + aim assist pull that gives you away, rather than someone who actually noticed you (although there is the occasional player who can discern between character and mannequin quick enough).