But the 77-year-old Carlisle woman says she left eight hours later with a 2008 Hyundai she didn't want and couldn't afford.
McKnight said a saleswoman pressured her to "try out" the 2008 Hyundai Azera with promises that she could return it the next day.
A sales manager at Holmes Hyundai secretly checked her credit while she waited for service on her car, McKnight said. The sales team also allegedly suggested that she could afford the newer car if she stopped paying on her Medicare supplemental insurance.
"I told them I cannot do a bigger payment," McKnight said. "I just kept telling that. They didn't care."
The accusations came to light in a Polk County lawsuit.
Max Holmes, who owns the dealership, disputed McKnight's version of events and said his lawyers will respond to the accusations in court.
He said his lawyers were trying to reach McKnight's lawyer to resolve the situation.
Holmes, in an interview Friday, said his dealership "tries to be straightforward and honest" and had been portrayed unfairly by the lawsuit.
"The important thing to me is that, since the day after she purchased her car, we've been working with her to try to accomplish her objectives," Holmes said. "We still will, and that's really our first and only objective here — to end up with a satisfied customer."
McKnight's lawsuit would have been much more difficult to file, if not for a state law that took effect on July 1. The consumer fraud law, hailed by consumer advocates but opposed by many business groups, allows Iowans to collect legal damages and attorney fees from businesses that commit fraud.
State lawmakers passed the law in April with near-unanimous support.
Iowa became the last state to adopt such a law, although the version lawmakers passed contains stronger provisions than similar consumer-fraud laws in other states, said Bill Brauch, a spokesman for Attorney General Tom Miller.
Consumer advocates have said the Iowa law offers too many exceptions for businesses. The exemptions include insurance companies, banks, lawyers, cable TV providers, doctors, veterinarians and architects.
McKnight's lawsuit is the sixth private claim filed in Iowa since the new law went into effect, Brauch said.
For now, McKnight drives to her job in West Des Moines in her brother-in-law's 1999 Buick LeSabre. The first payment on her new car is due Dec. 16.
McKnight said she arrived at the dealership around 8:30 a.m. Oct. 21 for an oil change.
A saleswoman approached McKnight while she waited, and asked about her interest in a car. McKnight said she had only come for the car repairs, and could not afford a trade-in.