"Hanif Is Carrying Out Research Investigating Unconscious Grocery Shopping Behaviours

"Hanif is carrying out research investigating unconscious grocery shopping behaviours. He has written consent from the store manager, a notice is placed prominently near the entrance to the store informing shoppers that a researcher is inside doing a structured observation of the numbers and types of shoppers that day." If we assume informed consent is not needed as a store is a public place, why could Hanif's research still be regarded as unethical?

A) Shoppers do not know if they are in the study or not
B) He is deceiving participants about the nature of the research
C) The methodology is flawed
D) Hanif will have a problem with "reactivity"