Hey all, I sold a car 3 months ago, I'm a private individual so not a dealer nor did I offer warranty or anything, the car was sold as seen with test drive offered and they had the option to have a mechanic come check the car over before purchase.

Now, yesterday they came back after nearly 4 months complaining that the DPF has been tampered with and that the gearbox has been giving them loads of issues, the gearbox was replaced in my ownership however I had not tampered with the DPF.

They've basically come saying they want a full refund and that I have to take the car back and refund them the full amount as they claim the car wasn't fit for purpose. However in my eyes, they bought the car, we're happy with it for 3 months and all of a sudden things have gone wrong with it and now they want their money back? I don't think they have a leg to stand on but I'm just needing some external advice too.

They also said it has had issues from the very start which if it had why not contact me sooner when the issues were probably smaller and easier to deal with rather than let it get to gearbox problems?

They've threatened getting a solicitor and all sorts but any advice would be much appreciated on what my rights as a private individual