I've mentioned this before on this forum...but it's important to always haggle...particularly when buying a significant piece of kit. Many retailer are desperate for business and commission based sales are often the best.
Also, be prepared to pay by credit card OR cash. Remember that a retailer has to pay around 3% of the transaction to Visa/Mastercard...so offer to save them some of this by asking for a further 1% discount.
On a purchase such as a car, this is actually a fair amount of money and might be the equivalent of three or four tanks of fuel.