Duplicate file cars in good conditions sell quick as they are in range of most buyers...
I personally have a 2006 Alto with duplicate book, original 24000 Mileage, and I have several offers. Likewise santros, cultus etc sell quick as they are 50,000 - 75,000Rs cheaper.
If u purchase it cheap, u can sell it at normal depreciation rate later. However if u bought a car with original book and lost its file, ur gonna suffer the loss! If u buy it at duplicate rate and sell it at duplicate rate nothings lost.