the pee discount?

A young couple were in my store tonight getting ideas for their wedding registry when they found a microwave that they just had to have.  It was the last one - a display - so I was going to sell it to them.  They asked if they could get a discount which was what I was about to offer as I figured out the percentage to dollar amount in my head.  As I was thinking, the man asked me to consider that people had opened and closed it a bunch of times and that someone might have peed in it.  Peed in it?  I told him that I could guarantee that no one had peed in that microwave. (we keep the crock pots out for that...)