Project Manager in

Took my lawnmower as it was still under warranty and wouldn't start, they called me about a week later to tell me there was stale gas in the Carburetor and needed to be replaced, not covered by warranty and extimated the cost to another $140 on top of the $54 I already paid when I dropped off the mower, I obviously declined. Took it home, sprayed some Carb cleaner in the carburetor and machine has been working beautifully since then. I should get my $54 back as is very clear they did nothing to diagnose the problem correctly by checking if the carb just needed to be cleaned instead of just assuming and suggesting to purchase a new one. What kind of technician does things like that?