I had a similar story with a Nation wide Garage
I suffered similar a number of years ago ........ My old Sierra needed a set of rear shocks for the MOT. Best price was from one of the " fast fit " style places, so after a phone call to confirm they had the parts in stock off I went. In the 10 mins it took to get there they were in the middle of fitting the only set they had to another car
They then proceeded to inform me the only set they had left were gas shocks and they were more expensive. I reminded them of the telephone conversation we'd had only minutes before and managed to convince them to supply & fit this set for the originally quoted price
Anyway .... fast forward 1yr and the same car needs a full exhaust system, so after a few phone calls the same establishment manage to offer me the best deal. Off I go again and after the exhaust has been fitted they inform me the rear shocks are goosed. Okay I say, just replace them like for like. I'll take the gas shocks .......... see their mistake yet ?
Once the car is off the ramp they present me with a rather large bill for the work. I retrieve my wallet and a receipt for the shocks from last year from the glove box. The shocks came with a 3 year guarantee. You should've seen his face
He then had the cheek to start shouting at me as I hadn't informed them the shocks were only a year old ......... I knew, as well as he did, there was no fault with the shocks.
His gaffer ripped him to shreds in front of the entire waiting room. A sweet moment indeed
Before I left I even had the cheek to ask for the new receipt which covered the shocks for another 3yrs.
Given that I'm ex-motor trade I sometimes think I do tend to take a bit more care when being informed of faults needing work. I always question their decision and ask to be shown the faulty part first. I've watched some individuals dig themselves some very deep holes before letting them know what I used to do for a living.