Ah, newbie questions.
The answer to your last paragraph is: It depends.
If you bought a sit-down Daytona racing cabinet. No it would not fit through your front door.
If you bought a mini cabaret style cabinet, yes, it would fit through your door, and even fit in the back of a wagon style car.
OK sarcasm aside... The average cabinet fits through front doors with about half an inch to spare. Those with wide control panels, you can remove the panels. But otherwise nothing else "breaks apart".
Measure your door ways, then measure the goods at the auction. You shouldn't bid on something you haven't inspected anyways.