The school asks for your reason of rejecting the offer is simply for their own record. They will use this information for future recruiting strategy. Unless you mentioned that you haven't made up your mind and there's a chance that you will take the offer if they increase the money amount, they are very unlikely to bargin with you  Just tell them that you have accepted the offer, and the reason is the financial aid amount between the two similar programs. The true respect is telling the truth and believe it or not, this information plays an important role in the school's future recruiting strategy. Each year many universities pay big bucks to consulting companies to find out where their accepted applicants went and why. After all, it is business and two-way selection, there's nothing about hurting the feeling although most of the times we do get hurt by the schools. | 
