I think if they fit new parts to your car and you then drive your car away without paying, then you'd be stealing the parts (but not the car). I don't know if the police would be interested or not, they might consider it a civil matter (i.e. it's up to the garage to sue you).

But unfortunately you are not paying them to fix it. You are paying them to work on the car to try to find the cause & to try to fix it.

They tell you what they think the cause is & you approve the work or not.

If it doesn't work it is still down to you, unless they have catagorically stated (which means you have it in writing) that they are certain that replacing the ball joints will rectify the problem.

Good luck

I disagree - but only from my point of view (I'm no lawyer). The garage carried out a thorough examination of the fault and told me (verbally) they had found the cause of it and what needed replacing to fix it. They told me how much it would cost to fix, I approved them doing the work. As far as I'm concerned, I entered into a contract for the garage to fix the fault; I did not enter into a contract for them to spend money on replacing parts on a try-it-and-see basis. They are meant to be the experts. I trusted their judgement. With the benefit of hindsight, I should have test-driven the car before paying them.

They did not categorically state in writing that replacing the ball joints would fix the problem, but there surely has to be a reasonable expectation that this is what I was paying them for - rather than just practice at changing ball joints.

I once had a washing machine fault. It was examined by a repairer, he told me it needed a new part and quoted the cost of the part and the fitting. When he did the work, the machine still did not work. I was not charged for labour or the part. Upon further examination, he discovered another part had failed - he got a new one, fitted it, the machine worked again, and I was only charged for the second part. How is this different from my car? The washing machine repairer took the risk - correctly in my view. In the case of my car, the garage is not taking any risk at all. Why should I bear all the risk?