You are responsible for expenses over the reimbursement limits established in this chapter. Your agency will not pay for excess costs resulting from circuitous routes, delays, or luxury accommodations or services unnecessary or unjustified in the performance of official business. Failure to provide sufficient justification to your approving official for such accommodations or services will limit your reimbursement to the constructive cost of the amount authorized versus the amount claimed.
41 C.F.R. §301-2.4