There are several ways to qualify for category upgrades. There are valid offers out there. For example Azamara is currently offering to house you in a balcony cabin by paying an oceanview (and sometimes inside cabin) rate. If you were to sail on Celebrity and gain status and join the Captain's Club you are also entitled to move up a category, within limits. Both are owned by RCI and offers do come and go. The Captain's Club offer is, for now, standard.
As for two for one pricing...that's another kettle of fish. We get offers from Viking Ocean, HAL, Oceania, Regent, Silverseas and Crystal etc. constantly offering 2fers but rarely see a standard rate. I don't consider this more than advertising. There is almost no way to compare standard rates.
The most advantageous offers seem to be on top of the individual cruise lines with sweeteners from cruise travel agents.
I wish someone would pick me up for a cruise. You've got great travel agent.