If I recall from business law, accepting part of what is due can make it harder to collect the rest. Your protection in such an instance is an invoice for the full amount, even one hand-written on the spot. You would mark it as partially paid, showing the balance still due, and leave that with the person who gave you the check. This reduces the problem administratively for the AD, who will appreciate a piece of paper to keep the accountant happy for paying twice for the same vendor, same date of service. Even a business card (with whatever you add on the back) can serve as an invoice in a pinch, and gee! I think I'll keep this in mind myself! :~)

In my case, it's donations toward mileage and other expenses that we accept-- and written documentaion clarifying this will become the norm for us.

~Susan