A one-on-one negotiation with a car dealer can be intimidating, and can influence a driver to make an unwise choice in his vehicle purchase. The main reason for this is that it's often difficult for the future driver of a new car to be fully objective about his purchase – when a potential buyer gets excited about a car, he may be more likely to overlook red flags during the test drive, or be pressured into buying add-ons he doesn't want or need.
A friend or relative brought to the dealership is more likely to keep a clear head about the purchase, according to Edmunds, and is less likely to let excitement about the prospective purchase get in the way of thoroughly evaluating the offer. The companion is therefore likely to spot inconsistencies during the price negotiation, and if he or she remains non-committal, the salesman is less likely to have the bargaining advantage associated with knowing that the buyer has firmly decided on the purchase.
Another way to take stress out of the negotiation is to come to the dealership pre-approved with an online car loan. With car financing in hand, the buyer and his or her companion can focus solely on the merits and disadvantages of the car itself.