No JDM motors are not rebuilt. They are low mileage used motors. Any JDM motor you buy will have at the most 60k on it. In Japan they are required to replace the motor or get a new car at 60k miles, its emissions laws over there, that all i know so dont hate. As a plus we get a large amount of very low mile used motors. All good JDM engine importers and sellers will do a compression test to check the motor before selling and most typicall come with some warranty. Can you get a bad motor yes i have seen it before but i have seen and installed many more good engines. Imo a JDM engine is a way better choice than a local wrecker motor.