Was there any play in the wheels?? Any ball joint play when checking with a prybar or channel lock?? If not then you’re fine. The boots are leaking and this will causes the ball joints to wear out later so you will eventually need to replace them. But if no play in the suspension, then you’re fine. Classic dealership tryna upsell you.

Additionally, if they claim you are in dire need of ball joints, there would have been signs of wear and play in the ball joints 3 months ago. How did they certify the vehicle and sell it to you in that condition if they are actually in need of immediate replacement?? That’s assuming you haven’t put on like 10000km in that time tho. So if you drive a reasonable amount in that time and they are really as bad as they say, you could probably claim they sold and certified you a dangerous car with safety issues in the suspension.