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."