This activity is 100% legal and there is no law that prohibits its execution.
Missions must be carried out incognito unless explicitly stated otherwise. This means that you should not ask permission to take pictures, but discreetly try to take photos without being seen.
The rules imposed by shopkeepers on the ban on taking pictures have no legal basis, but as a company policy our advice, in case of unpleasant situations, is to abandon the mission and the workplace and send an email to support.
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