WASHINGTON – Heading into the final stages in overhauling financial regulations, a joint congressional committee is ready next week to tackle one of the thornier issues — whether car dealers will be regulated by a proposed consumer protection agency.

The joint conference committee is wrestling with the role dealers play in auto financing and the discretion they have to set terms — and potentially take advantage of consumers.

“Car dealers are out there shopping for the best rate for themselves and they don’t pass that on to the consumer,” said Tom Domonoske, a Virginia attorney who works on auto financing issues.

Dealers that assist in financing argue they’re just middlemen in the process, helping buyers secure the best loans. Abuses are rare and already covered by anti-fraud regulations enforced by state officials and the Federal Trade Commission, the dealers said.

As savvy car buyers armed with online price data and other information have pushed for harder bargains on purchase prices, dealers have tried to boost other sources of income, such as service contracts and auto financing. In some cases, consumer advocates said, they’ve resorted to questionable tactics.

In need of a car, Sara J. King of Encinitas, Calif., went to Toyota Carlsbad with her parents in March to see if she could make a deal. But with poor credit, she found the best interest rate too steep at 16 percent.

As the dealer was preparing to close for the day, however, King, 26, said the finance director made her an offer she couldn’t refuse: Drive home in a shiny new white Corolla for $3,500 down with 0 percent financing.

“They said, ‘We’ll make it work, we’ll make it work,’ ” she recalled.

They didn’t. Ten days after she signed the paperwork and pocketed the keys, Toyota Carlsbad told King that it couldn’t find a bank to take the loan and that she’d have to agree to 16 percent financing.

Consumer groups said King’s experience showed the need for more government oversight of auto dealers.

Her case is an example of what the industry calls yo-yo financing: A dealer agrees to a great bargain, then pulls it back a week or two later. The goal is to get the buyer to pay more later to avoid the hassle of returning the car.

“I said, ‘No, this is not my fault. You called me days later in hopes I’d love the car and just pay the price,’ ” King recalled.

She returned the Corolla and got her down payment back.