In the absence of a CEL and accompanying DTCs, I’d say them confidently diagnosing the culprit to be injector failure seems improbable.
They might want it to be bad injectors since that would provide the best opportunity for a large repair bill, but there would be a lot of labor involved to accurately pinpoint the injectors as being bad, and you have given no other indication that they are more likely to be bad than something else. So why would they automatically jump to checking the injectors first?
I hate to indict anyone without sufficient evidence, so I won’t state for the record that I believe those folks are being dishonest with you. However, I will absolutely say it sounds like they are being lazy at the very least.
Asking them to provide you with more info on how they arrived at their conclusion seems perfectly reasonable to me, especially considering the significant amount of the repair bill if you approve new injectors to be installed.
If they aren’t willing to provide that info, I say punt and go somewhere else.
