1. brand certification: Bach trumpet generally has a brand logo, which is usually printed on the trumpet shell. Brand certification can not only prove that this trumpet is a real Bach product, but also provide additional quality assurance.

2. Serial number: Some Bach trumpets will have a unique serial number, which can also be used to verify the authenticity of the trumpet. If the serial number can match the brand certification, then this trumpet can be considered as a real Bach product.

3. Manufacturer: When buying Bach trumpet, make sure it is produced by a regular Bach manufacturer. You can check the information of the licensee through Baha official website or other official channels.

The above methods can help you identify the authenticity of Bach trumpet. If you still have questions, it is recommended to consult a professional.