It would help to know where you are bare boating and which company you are chartering from. The big boys; Moorings and SunSail are extremely professional and 'usually' hand over the boat is ready condition. Should run into trouble with the boat you can't resolve yourself, you radio them and they'll send assistance ASAP. Getting familiar with a boat that is configured a bit different than your own shouldn't be too hard. Pay particular attention to the anchoring procedure, which can be different to what you know, as well as the mainsail reefing procedure. Other than that, the charter company should be providing a good manual to boot!
S/V Don't Panic!
ďNavigare necesse est, vivere non est necesseĒ To Sail is vital, to live is not.