if that blade is stainless, it is very unusal in old saw blades,but if it was carbon ,the higher the carbon content the sooner the rust,the only way i can think that would have rusted that soon, if it was stainless of a high grade, would be contact with salt water.surface rust can be cleaned off,doesnt make it a bad knife,is it easy to sharpen will it take and hold a good edge thats more important than a bit of corrosion especially for the price. if he really just wants his money back id clean the knife up re sell it,take expenses and time out and give him the balance.put it down to experien