TULSA, Oklahoma - Charlene Mann is guardian and caretaker for seven of her grandchildren. If she wants to take them anywhere, they have to walk or catch a ride.

Mann's '03 Ford Explorer broke down last winter.

"That was the only way to get them to the doctor, to school, to sporting events," Mann said. "I don't have that now."

She saw a post on a neighborhood Facebook group from a man named Deryl Keifer advertising his mechanic services.

Mann said she called Keifer, who advised she needed her car's engine replaced. Mann's extended warranty company, Route 66, approved Keifer, who agreed to replace the car's engine.

That's when things seemed to go off the rails, Mann said.

"He came by a few days later with a blank invoice," she explained, "And he had me sign my name, told me that the warranty company needed my signature to verify it was okay he worked on my vehicle."

Essentially, Mann claims, Keifer asked her to sign a blank bill for the warranty company's sake. She said Keifer took that money from the warranty company but never actually did the work, never returned the car, and then he ignored her calls and texts.

Mann said Keifer had her car towed from place to place. Eventually, she tracked it down to Southwestern Motors in midtown Tulsa.

Trevin Martin owns Southwestern Motors and has been looking after the car for months. Martin said he started working on it, but said Keifer flaked on him, too — promising to pay him to replace Mann's motor but never giving Martin any money. He and Mann speak regularly to update each other on the situation.

"Guy seemed awful shady," Martin said of Keifer. "I told him he needed to bring at least half [the payment] down before he went any further. Months went by - he lied about when he was going to be here."

That's why, months later, Charlene's truck is still sitting at Trevin's shop — without an engine.

Of course, News On 6 wanted Keifer's side of the story, so we called him.

First, Keifer said he had nothing to do with Charlene's car — even though Keifer's signature is on the warranty and Martin confirms he dealt with only Keifer during their interactions.

"They didn't pay me, they paid my father. My father's the one that did it — not me," Keifer said.

Then, he cursed.

"I don't give a f*** who y'all put this on the news to," Keifer said. "I hope you do put it on the news."

And finally, he threatened to sue.

"This will end up in Small Claims Court through slander," Keifer said. "Because y'all are airing slander on air."

Mann believes this is a lesson: only go to a reputable mechanic, and never sign a blank invoice.

"Hopefully, I can keep this from happening to anybody else," Mann said. "That's all I want."

News On 6 left a message with Route 66 Warranty, but their offices had closed. We also spoke with several other people who said they had similar experiences with Keifer.

Tulsa police said citizens can file a police report, but this is a civil matter best dealt with in Small Claims Court.