Let them you know you are a serious buyer and that you're ready to buy now. Then get the best deal and leave. When you come back in two or three days, wait no longer, you'll get a better price. Do not tell salespeople that you are shopping. The best time to buy a car is one week before the end of the month or a big holiday, such as New Year.
Most dealerships have a quota.
They need to sell a set number of vehicles per month. Always test drive the vehicle for comfort, noise level, power, and braking. If the vehicle doesn't feel right to you in any way consider another car. Get a copy of everything you sign at the time you sign it. If there is a problem later, you'll have the paperwork.