TRAVERSE CITY, Mich. -- Phil Awker's ad for a used 2004 Chevrolet Suburban has been languishing in an online classified for more than two months, even though it's priced $6,000 less than book value, according to USA Today.

Billy Roach's 2002 Jeep Wrangler has been up for a month on Philadelphia's Craigslist. He just wants to pay off his loan, Roach says, and he's hoping to get about $10,000 for it. Book value is about $2,000 less than that.

Such situations are popping up all over the country, and automakers worry that declining residual values -- how much vehicles are worth for resale -- will embitter their customer base.