TrueCar (TRUE), an Internet-based venture based on creating price transparency for shoppers of new and used cars, has seen the price of its shares double from the initial offering price over the past six months. The company decided to exploit that runup, announcing last week that it sold another 6.4 million shares to the public.

One million of the shares were issued by the company; 5.4 million shares of the offering come from existing shareholders, including its largest, San Antonio-based United States Automobile Association. Scott Painter, TrueCar founder and chief executive, bought $500,000 worth of stock.

The secondary offering coincided with expiration of the so-called “lockout period,” before which insiders were precluded from selling shares.

Scott Painter, TrueCar chief executive officer, expressed satisfaction that the company’s share price remained strong through the secondary offering.

“We were able to successfully manage that process in a way that resulted in not a dip, but a nice gradual appreciation, and to successfully allow the employees that wanted to get liquidity on the day of their lockups expiring, to give them flawless capability to do it,” he said.

TrueCar was founded in 2005 and has tweaked its business model several times during the past decade in order to comply with state laws and to avoid antagonizing dealers.

The $70 million the company raised in its IPO in May was relatively small, creating a public market for shares and greater disclosure of the company’s performance. The funds were used in part to pay for advertising, raising TrueCar’s profile and helping to attract customers to its website. Its latest financial report suggests the strategy is working: TrueCar posted third-quarter revenue of $57 million, up over 51% from a year earlier; users on TrueCar’s platform accounted for 172,000 sales in the period, up 47% from a year ago.

TrueCar’s analytic software, which relies on recent transaction prices gathered from dealers, allows shoppers to discover what it calls a “fair” price that is close to the transaction prices of similar or identical vehicles – almost in the way that securities prices are divulged. With this information, the shopper can arrange through TrueCar to buy such a vehicle at one of its 9,000 certified dealers. The dealer pays TrueCar $299 for each used-car transaction, $399 for each new-car sold.

Though TrueCar acts as an intermediary in the sale, it’s careful not to call itself a “broker,” a term that might bring it into conflict with laws in some states.

Some dealers identify themselves as anti-TrueCar because profit margins on new and used-car sales have been shrinking, in part due to more accurate disclosure of recent transactions. TrueCar argues that the same reporting can be helpful to dealers, too, helping them to avoid pricing mistakes when selling cars.

Another big change in automotive retailing could be unfolding with the announcement by AutoNation, the nation’s biggest publicly-owned chain of dealerships, that it next month will demonstrate a “digital storefront” that allows shoppers to inspect its inventory of cars, fill out paperwork and reserve a vehicle – all on line – on at a specified no-haggle price. The company said it has invested $100 million in the technology.

But many dealers insist that traditional customer visits to their showrooms and haggling sessions with their sales personnel won’t disappear anytime soon. They’re backing that opinion with sizable investments in stores that are bigger and glitzier than ever.