i've owned several cars, some 2nd-hand, since i started working 25 year ago. each time i sent the car to the workshop, parts were changed with minimal hassle & i have very few grouses with the workshops. that, perhaps, is because i make it a point to send to the dealers' workshop.
how would you react if you sent your car for a part replacement in the morning & sometime at noon, the service guy phoned you & told you they didn't have that particular part? remember, they made that appointment with you on the premise that they will get the car fixed.
how would you respond, considering that they've literally taken your car apart & then found out that the spare part was not in stock? & to rub salt into the wound, they enquired if you'd settle for an inferior part?
so, you are wondering - where's the analogy here?
well, how about this.....
you go for an operation in a private hospital. the surgeon opens you up. the assisting nurse tells the surgeon they don't have an essential piece of equipment in stock. then she asks the surgeon, would he mind modifying his procedure to accomodate an alternative but inferior device?
this, of course, is only an analogy of a hypothetical event.