Sold A Car And They Want Their Money Back.

Location: Maine I bought a car on marketplace for next to nothing that would crank over but wouldn’t start. I bought it from a guy that bought it for scrap. He had a signed title with a blank slot for who it should be assigned to. I made it run and fixed some cosmetic issues and listed it for sale. A couple in their 60s showed up the next day and looked at it. I told them I’ve never driven it because I’ve never registered it but driving it around the yard everything feels good. They left and scheduled to have their mechanic look at it the next day. He looks at it and says the car is clean for the age and I was asking a fair price. I was asking mid 6000 range and took high 5s for the car. I gave them the keys and the title that I was given. They asked for a bill of sale for it. I handed them a blank sheet of paper which he filled out with the year, make, model, vin and mileage. He did not write out as is where is. I didn’t care because he then forged the original woman’s signature on the bottom so at no point have I signed anything. They get it insured and leave to go directly to town hall and register it. I get a phone call around 9 the next morning from him stating the car will not start. The lights don’t come on it does nothing. I informed them that I was busy for the day. and to call their mechanic who came to looked at the vehicle and have him see what’s wrong with it. It was implied that I would look at it at some point in the future if he couldn’t figure it out. Within 5 minutes of hanging up I received another call stating he didn’t answer and the I “need to come look at it” I reiterated that I was busy and to contact their mechanic. Over the next 6-8 hours I received over 15 phone calls with multiple text messages. I informed them that I had been busy all day and they promptly informed me that they’re sick of the car and I need to bring a trailer to their house with their money and pick up my car. I informed them that would not be happening because I do not want to purchase the car and it has been registered so they do not have a title to sign over to me. I informed them that when they buy a car from a private party it is their responsibility as soon as they take possession of it. Furthermore they had their mechanic look at it and say it’s good and they drove it home. I was informed I am not a man of my word and that I’m a scam artist. I was informed I would be taken to court for this. I was informed they would be making Facebook post about me and that they would be showing up to my work (my dumbass was wearing a company shirt when they were here) on Monday morning to speak with my boss and see how he feels about it. This was all 2 days ago. I have spoke to my boss and he said he’s not worried about it. I woke up with a business card for the state police stating to call dispatch and request a certain officer. I called under the mindset of this is strictly to build a case against me and don’t say anything beyond “I’ll need to speak with a lawyer before answering any questions” I spoke with dispatch and was informed he is off duty currently and won’t be on duty till 7am Sunday and to call back then. Should I call back? I didn’t have it titled in my name so I never paid sales tax so I do feel I have done something wrong. Honestly not sure what to do.