Editor's note: An earlier version of this story mischaracterized the role dealers play in Trade-in Marketplace and the share of vehicles bought by dealerships or traded to dealers under the program.

Shoppers using the Trade-in Marketplace on Autotrader.com soon will see Kelley Blue Book values when they request an estimated value for their trade-in.

Cox Automotive Inc., parent of Autotrader. com, Kelley Blue Book and other well-known brands, wants to cross-pollinate its units' tools. In doing so, Cox, along with other third-party vendors, is seeking to navigate its way to a larger role in auto retailing. But missteps in doing so can easily alienate those vendors' dealer partners, as Cox discovered recently when it caught flak from dealers for a program that showed wholesale auction prices to consumers.

Following a pilot this summer, Autotrader.com is adding Kelley Blue Book values to its trade-in valuations nationally. At the same time, Cox is rebranding the Trade-in Marketplace to consumers as an "Instant Cash Offer" on both Cox's and dealerships' websites.

Jeremy Beaver, vice president of Del Grande Dealer Group, of San Jose, Calif., said the Trade-in Marketplace has been a fixture at the group's 14 dealerships for the last three years. Whenever a customer with a trade comes in, a staffer goes to that site, KBB.com or the dealership's website to determine the car's worth.

Jared Rowe, president of Autotrader, said the tool is meant to bring transparency to what an Autotrader study has found to be one of the most stressful parts of buying and selling cars: agreeing on a trade-in price.

Until recently, values yielded by Trade-in Marketplace tended to be lower than those on Cox's Kelley Blue Book, Beaver said. But as Trade-in Marketplace has been refined, the differences have narrowed, so now Cox can show the Kelley values side by side with the Trade-in Marketplace ones.

In addition to using Trade-in Marketplace with showroom customers, Del Grande uses the tool to find and buy used vehicles.

The group has a seven-person center for buying used vehicles for the stores. Of the nearly 200 the center buys each month, about 80 come from people who negotiated a price on Trade-in Marketplace, Beaver said.

Rowe said 2,400 dealerships that participate in Trade-in Marketplace offer to buy about 250,000 vehicles per month from customers who complete the Trade-in Marketplace process. Of that number, about 23 percent of those cars are bought by dealerships or they are traded to the dealers. That's up from 16 percent a year ago, Rowe said.

Not all pilots end as well as the Trade-in Marketplace enhancements, however.

A separate Cox experiment that briefly gave Atlanta residents direct online access to vehicles held at Manheim auctions has been shut down. Cox owns Manheim.

Under that pilot, consumers responding to Facebook ads could go to readysetcar.com and select a specific auction vehicle. They then negotiated a price with one of two franchise and five independents dealers in Atlanta. The dealer would buy, or attempt to buy, the vehicle at auction for the customer.

The pilot ran for about 60 days until it was terminated in late July, when dealers beyond Atlanta complained after hearing about it, said David Liniado, Cox's vice president of New Ventures.

Cox never sold the vehicles directly, he said. The idea, which came from an internal Cox innovation contest, was to find used-vehicle shopper prospects for participating dealers by getting those consumers interested in specific auction vehicles, he said.

Todd Caputo, owner of Sun Chevrolet and two used-car superstores in Chittenango, N.Y., said Manheim's wholesale auctions should not have been open to the public. Manheim has been right through the years to limit them to dealerships, brokers and wholesalers, Caputo said.

He said he was especially irked that Manheim showed shoppers the estimated prices that like vehicles had sold for at auction in their markets.

Caputo said that level of transparency threatened how much dealers could mark up the cars above what they paid for them. "We're talking thousands below what they retail for," he said.

Caputo said he appreciated that a senior Cox executive called him about his complaint and the site was taken offline about two weeks later. Readysetcar.com now states the program is "back in the lab" for further development.

Liniado said he didn't have a count of how many cars had been sold through the program. He said the program could be tweaked and eventually resurface. Liniado said some Atlanta dealers not in the pilot wanted in after hearing about it.

Cox Automotive has a history of piloting new programs frequently, not all of which succeed.