When the sub can't sell a hand-me-down for the sum it expected--known as the residual value--the shortfall shows up as a loss.

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That means if the maker subsidizes the residual, it only has to reserve for the coming loss at 50 cents on the dollar, which is a lot cheaper than a few thousand dollars cash in rebates.

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We looked at residual value predictions for 2013 models compiled by Automotive Lease Guide and personal injury claims data from the Highway Loss Data Institute.

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