LBS like these need to die. Show me a carbon wheel that isn't made in China. Show me a hub that's not made in China.
Anyway.
Trace velo has a recent video where he thought he got a bad cassette, when it was a MTB type cassette that just needed a spacer to fit on a road hub.
My 5 cents: switch to waxing your drive train (plenty of videos on YT on how to do that), and now that your drivetrain is always clean, do your own basic maintenance like changing cassettes and what not. You really dont need many tools, will grow hair on your chest, and will make you 12% more attractive.