Salesman: "Hey buddy, do I have a great deal for you! I'd like to lease you this fancy new Field Detector sensor for your ship!"
Ship owner: "Ummm ... not sure ... budgets are kinda tight ... but at the same time, them pirates keep lurking and hitting my support ships, so ... I am kinda in the market. Still, I'm worried about cost ... how much is the maintenance on this here sensor?"
Salesman: "Negative zero point three."
Ship owner: *bewildered* "Did you say ...... negative ....... as in ..."
Salesman: "Yes, negative! We send you a check every week, instead of you sending one to us. We think this'll be fantastic for our sales!"
Ship owner: "I definitely think it would .... but I can't figure out how you make a profit on that ..."
Salesman: "It's a secret to everybody."