I'm sure the right "whoever" can fix any carb but sometimes a carb just has gremlins. Maybe its got a manufacturing flaw? Who knows. My old Jeep never ran right. Had the carb rebuilt by a real reputable guy. Ran better but not the way it should. Finally I just bought a new carb. Ran great and never looked back. I'm also sure there are 10 people who will say that's bull and it just wasn't rebuilt correctly. Maybe so. But the new one saved me a lot of time and energy. In the end it cost about 2x as much as the full rebuild.

I also think most people just don't fine tune a carb correctly. I know I struggle. When I got my Bird, 2bbl, one of the screws was out 5 turns too far! I set it to factory and it ran terrible. Eventually we got it dialed in. More or less! Give me a lawnmower and i'll make it purr. Automobiles... ugh.
And as mentioned already you've got fuel filters, fuel pump, fuel lines, gas quality, timing and ignition system... etc that can all cause problems individually or several in combination. Heck maybe you got a bad spark plug or a bad wire?