Street vendors understand this. Yes, they try to entice you with an attractive product or a good price, but where they start is with you, engaging you with a smile or a comment, catching your eye or asking you a question. They know they have seconds to establish a relationship in which you will want to buy from them rather than the next vendor down the street.
In your work and personal life, where the relationships endure for many negotiations, you need to be aware of the impact of your actions on the relationship. What you do today will be reflected in how people respond to you tomorrow, or if there will even be a tomorrow in which to negotiate.
Of course, not all relationships are important to the same extent, and sometimes the outcome of the negotiation is so important that you need to negotiate hard even if you damage the relationship, but it is always important to keep the relationship in mind and to be deliberate in your actions.