I can't blame you for being angry. Even if the test was negative for Ringworm, a vet with very much experience should have recognized the symptoms and possibly done a trial treatment just to see if it would help.

Where I work they also sometimes use a Woods Lamp (blacklight) to help in diagnosing Ringworm. But often they'll pull on years of experience with the symptoms despite negative test results and have had much luck with it.

I don't know that your bad experience with vets is just greed, or a fear of making a medical decision based on experience vs having proof positive lab results to confirm them. Sometimes vets, and human doctors, get so frightened of not being 100% positive on something until they have lab work to back it up that they won't do anything without it. I think it hinders them.

Glad to hear that after all that your dog is scab free now.