Disney absolutely does NOT allow any discounting whatsoever. They require everyone to sell the same cruise for the same price, period. If any discounts such as Military Rate, Senior Rate, Resident Rate, etc. are offered, everyone can sell these. But Disney is very strict about this, so you will not find any other non-authorized discounts. If you do, be VERY careful because that company is in violation of Disney's policies and could have their credentials taken away - obviously, not someone you want to do business with.
So best advice, work with a reputable travel agent, preferably a Cruise Specialist, and know the price that's advertised on the DCL website is exactly what you'll be paying. But you do want to work with an agent as they represent you and should you encounter any problems, their resources can be invaluable to you.