Tyre fitters/mechanic - am I being swindled?

Hi all.

So, a few weeks ago I left my 2007 Audi 2 litre Diesel with 308,000 km (or thereabouts) in to a tyre place to get 4 new tyres.

The place showed me I needed a new piece for the CV joint and brake pads and they said they have a mechanic who does jobs for them. That was fine as I knew about the brake pads so I told them to sort both jobs.

In the meantime the balance was off on my wheels after the new tyres were put on as there was vibrations coming up through the steering wheel. When I left the car in for the mechanic to do the couple of jobs I told them about the wheel balance and they said they would sort this.

I then collected the car and the balance was still off. I couldn't get back to them straight away to sort this but I called them about it and they said to just drop the car in any morning and they would sort.

I finally got around to that today and they showed me that the ball joint was going on the side that they fixed the CV joint on. It was a different person to who I was originally dealing with who did the wheels today and showed me this and I told him about the CV joint and brake pads and he said he can see they were done and he can't say anything about the ball joint not being seen a few weeks ago but it is going now.

Now, they are a big enough place with a good few staff and they are there years and also my car is quite old with high mileage so I suppose these things can go, am I being paranoid in thinking they tampered with my car and are trying to make a few extra quid?