This is why it's always best to book with a reputable agent as they would have explained all the good things/bad things associated with booking a 'guarantee' cabin.
The good thing about booking a 'guarantee' cabin is the price. You can definitely save money on these.
However, the bad thing is you never know where you're going to end up. You could be in the front of the ship, where if you suffer from motion sickness is not a good place to be. You could end up in a partially obstructed view cabin, which could definitely take away from the enjoyment of being on a balcony. You could end up above, below, or next to a noisy area, which could impact your quiet time.
Now, with all that said, the type of guarantee you purchased will dictate the type of balcony cabin you get. Again, your agent will be able to tell you which guarantee you purchased. If you bought an oceanview balcony guarantee, then you won't get an inside balcony. If you bought an inside guarantee, then you will normally get an inside balcony, although sometimes you might get an upgrade to an oceanview balcony.
Once you've gotten your cabin, which is usually about 30 - 60 days prior to sailing (but can be more or less than that depending on the sailing and how well it's selling), sometimes your agent can get a change if you're not happy with the location. If you didn't book it with an agent and call the cruise line, often they'll tell you that you can't change cabins. (Agents have resources not available to you.) But whether you can get a change is often dependent on how full the ship is and whether any other cabins are available.
Bottom line is, if you get something you don't like, it never hurts to ask for a change.