Put it right back on their porch with a short note. Say something like 'Not a repair service, sorry.' Did that when a guy left a blender at my door. It stops the problem fast. They usually get the hint and don't do it again. If they ask, just be firm but polite.
My buddy Mark had his toaster break down last week. He stuck a post-it on it with 'fix this pls' and left it by the dumpster. Management swapped it out the next day.