TrueCar only gives you prices that people are paying for a specific make/model car, then suggests a "good" number based on the median. It makes money from generating leads and converting those leads into customers.
Visit Edmunds.com and calculate the "invoice" price of your vehicle with options. That's where you should start the negotiating. That's not the true cost of the car for the dealer. Aim for 5%-8% below "invoice."