One important condition for covert hypnosis (or conversational hypnosis) is a comfortable environment.
If a hypnotist were to corner a person or take the person to an unfamiliar environment, the person would feel insecure or even feel intimidated. Under this condition, the hypnotist will find it difficult to hypnotize that person.
It is a better choice for the hypnotist to allow the chosen person to choose his own venue as this would allow the person to feel much more comfortable and trusting. Since he is the one making the decision, he will feel more in control.