What do you mean by "spiff" here? Google doesn't give me any clues, and the only Spiff I know of (as opposed to the word "spiffy", meaning well-dressed) is Calvin and Hobbes' Spaceman Spiff.
A spiff is a free giveaway attached to a sale, historically a bonus for salespeople for making the sale but colloquially also for customers getting a freebie item with a purchase.