I call it normal.
Many computer problems are misdiagnosed due to incompetence, software glitches, etc. I can't tell you how many times Spinrite or other disk diag software passes a drive and yet it won't install windows, but a new drive will. And vice versa.
I own a computer shop. I see this all the time when people bring me a computer and ask me to check another shops diagnosis. It is startling how often they are wrong. Most of the "techs" who work on computers are not techs, but good computer users. They have no training nor certification.
Unfortunately it is almost impossible to prove the computer shop committed fraud.
The only solution is to take to, at the least, an APlus certified tech. And you should try and find other peoples experiences with that tech.
FYI I have owned my computer shop for 11 years. I have seen, seriously, 10 computer shops open and close in my town. Not one of them did a consistently good job. In fact, the large shop that opened a couple of years ago has finally blew thru all the P.C. users in town with thier incompetence. So two days ago they became an Apple store.