Aaron Kessler:

Third-party websites like Edmunds.com and TrueCar have upended the car-shopping process by offering similar features on a wider scale, which give consumers far more negotiating power than in the past. Not only can consumers research vehicles, but they can also get binding quotes from multiple dealers, without ever leaving the house.
 “It cuts down on a lot of the headache involved,” Mr. Isac, the Houston car buyer, said.
 Avi Steinlauf, chief executive of Edmunds, said some consumers show up knowing more information about a vehicle than the sales representative. “But the forward-thinking dealers are adapting to this and embracing the technology,” he said. “And they find they’re making more sales than they ever did before.”
 Despite his company’s role in shifting the balance of power, Mr. Steinlauf said he believed dealers continued to play a vital role.
 “You’re still talking about the second-largest purchase most people make,” he said. “Many consumers still want to touch the vehicle, sit in it, smell it.”
 But the nature of the interaction between buyer and seller is changing.
 “The salesman is really transitioning into more of a product specialist,” said Mr. Szakaly, the N.A.D.A. economist. “It’s not about someone who’s there to haggle with you; it’s about having you come in wanting to know about a product you’re already decided you’re interested in buying.”