A person "invites" people into 4 zones around their body.
0-18" is the Intimate Zone - people you really trust
18"-4' is the Personal Zone - people you trust
4' - 12' is the Social Zone - people you are not close to
12' + Public Zone - speaker distance from audience
The most important reason any agreement is made is trust. If a person does not allow you withon their Personal Zone, chances of an Agreement are greatly diminished.