Both parties are responsible, and if you have a good sound check it should be no problem. Having your own sound guy mix is great, if he respects and works with the house guy (who might own and be responsible for $$$$ worth of house gear. No, your stoner buddy cant set his beer on the board and twiddle knobs). Your guy knows what's coming and can bring up levels for you. Or its your PA and he knows it and runs it every time.
But let's get real, they throw your stuff up there, you get a line check, (maybe) and your off to the races! Its mostly on you! Once your stage volume creeps up, or if you just plain insist on your backline being super loud, or your drummer is a moron who only plays loud and louder...the sound guy can only do so much. And if you can't wrap your heads around the concept, he'll most likely stop trying and head out for a smoke. That's why that feedback won't go away...
If you hit the sound guy with a surprise peak, you better be lucky and hope that he's: standing at the board, paying attention, and isn't fed up with your schtick.
Almost always, the first culprit in the bad sound scenario is too much volume on stage from the band. If someone asks you to turn up a bit, you are on the right track.