In some states it is illegal to take money from the selling dealer to help a consumer. In other states dealers have generated laws to outlaw brokers. Don't be fooled by the service that charges you nothing to find you a car. They are a freelance salesperson, consultant or brokers, they are looking out for themselves and you'll get what you paid for, nothing. Trust that the dealer who gets the sale is paying this consultant handsomely.
Consultative sales are an oxymoron.
You can't be consulting someone on a sale if you have a vested interest in the outcome of the transaction. Be sure the transaction is separate from the money paid to your helper. Even the hallowed credit union folks are often making money on your car deal. The selling dealer is paying them for your referral. Banks, automotive clubs and similar groups can line up with those on the dole.