Well I had $75 onboard credit on the Inaugural Valor Voyage.. My TA offered us some and then because we were past cruisers we got an additional $25. So to all the SMART A**** on this board.. Yes it is possible.. Ask your travel agent and keep calling carnival who runs specials all the time.. The Carnival past cruise credits came 4 months after I booked.. I kept watching.. also my Cruise price went down twice and I saved a couple of hundred dollars on our cruise. My TA honored every price change that I found on my own by repeated calls to carnival and reentering my cruise info in their web site to see if my stateroom price had changed.. Your travel agent can't really watch for these price changes. that is up to you. Also every time my cruise price changed I also got money back on my Travel Insurance..
And I just plain asked to get an onboard credit from my TA..Now maybe for a honeymoon they would put a bottle of champagne etc.. or something like this. But every cruise I have been on I had received some sort of gift from my TA> So to all those NAYSAYERS.. I stick out my tongue!!