Is there a way to get an upgraded cabin on a cruise ship?

 I have taken about 40 cruises (stopped counting so am not sure) and have gotten lots of upgraded cabins. Why?  Here's why I think I have gotten upgrades:

1. I typically take a guaranteed cabin in the cabin category I am willing to live with during the cruise. I prefer an ocean view or balcony and am not bothered if either are obstructed. If picking an obstructed cabin number I check on cruisemapper.com to see if they have pictures or videos of the view.  If I take a guaranteed obstructed ocean view I have found that Princess, NCL and HAL have given me a "within cabin category" upgrade. This means I will get a better location on the ship or often an unobstructed ocean view.  I only once got upgraded on HAL to an balcony from an ocean view guaranteed cabin.

2. When I have taken an inside guaranteed cabin I have also gotten a "within category" upgrade but never and ocean view or balcony as I have paid a low price.

3. As I get to higher levels in the loyalty programs of the cruise lines I think they have taken into account my level as recently I have gotten upgraded from ocean view to balcony but I also think this is due to the two other things... the ship being older and the sailings have not been full.  This is key as you will not get an upgrade if the sailing is popular.

4. Cruise lines definitely take into account how much you paid for your cabin. The more you paid the more likely you will get an upgrade as long as the ship isn't full. As I typically use the cruise lines' air, buy an internet package and do the transfers and one or two shore excursions, this also adds up to the total spend.

5. I own the cruise line stock (100 shares), and this gives me onboard credit and I think might be in the mix for the upgrade decision. 

6. I use a travel agent and the cruise lines like to keep them happy. I have not gotten an upgrade when I booked directly with the cruise lines. I wonder why as then they keep all the money?

7.  Don't try asking for one, just have your travel agent tick the box that your open to an upgrade. I have never gotten an upgrade by asking for one.

Hope this helps

Marcia