Walmart sells its gas cleaner or injector cleaner for 97¢, injector & carburetor cleaner for $1.88; the prices for the STP are similarly proportional; the prices for the Gumout brands inverse. I’m no expert, but I always thought these were the same stuff with a different label. They list the same ingredients (‘petroleum distillates’ - not specific) and promise to clean similar surfaces.
When I re-built my carburetor earlier this year, the first time in 30 years, it looked clean. I didn’t even see varnish. I have used gas cleaner or carb cleaner about every year, but I expected some gunk to have accumulated.