Tesla offers customers who purchase Model S through its financing program a guaranteed buy-back. That is between 36 and 39 months after the purchase date, a customer who purchases a Model S through one of Tesla's two affiliated banks (which do offer competitive interest rates), Tesla will repurchase that customer's automobile at the greater of about 50% of the original purchase price, or the highest resale value of any Merceds Benz, BMW, Audi or Jaguar sold in that same year.
For this question, you should estimate the percentage of vehicles tesla will sell through its financing program, how many of those customers will resell their car to Tesla, and how much Tesla will lose on each repurchased vehicle.