Book the cruise yourself on the Disney website (pricing is same everywhere), and then see which agent will give you the most back and transfer to that agent. Transfer must be done within 30 days, after deposit is paid and before final payment is made. There are some agents that will supposedly give you more back, but I always use Costco and get around 10% back (8-8.5% in Costco gift cards, and 2% executive member refund. I personally would prefer to have Costco gift cards than the OBC, especially with some of the other cruise lines who have packages with included gratuities/alcohol so the onboard credit usage can be quite low. Costco also does not reduce the rebate if I transfer the reservation in like some of the travel agents do.
It seems like you have a pretty good idea of what you want and it is available elsewhere, so no point in dealing with an unresponsive travel agent who is getting 15% commission on the booking but is still uninterested in helping you, especially when a delay could cost you in terms of increased fares. If this person is so unresponsive before even booking, just imagine the level of responsiveness when you are past the refund period. It looks like the OBC from this agency is 5%, you can do better elsewhere and from your post it seems the service provided is not making up for the lower rebate.
