A Man Is Refusing To Give Back My Mother's Car While Increasingly Claiming He Is Doing More Repairs She Did Not Ask For

So, my mom just got a vehicle from a private seller. She took it to a friend of her boyfriend's who claimed to be a mechanic, to take a look at a few noticeable issues the car has. It has been nearly a month now and he refuses to give the car back, while also claiming she owes him $600 and claiming he has done $5000 of work on the car. She just wanted like two things checked out, relating to one of the windows that did not work and a possible wiring issue. He has claimed he has done an oil change, along with a bunch of other things she did not ask for. She just wanted it to be looked at for inspection, which time is running out for to be done. She has also informed me that he had her sign a torn off piece of paper that had nothing else on it, which we are assuming he could be writing stuff down on it as he finds more "repairs" to do. The cops told her they can not do anything for her. So now I'm just looking for legal advice on what can be done in a situation like this.

She is in desperate need to get that car back. She just got it so she could finally go back to work after not working for a long time due to a spiral of problems. She lives in low income housing in a small town without decent public transportation and low amount of businesses. She also has my teenage sibling to take care of, but is barely able to. So clearly she can not afford a huge repair bill full of repairs she did not ask for originally, but could possibly be forged thanks to her stupid actions