The judgement (Urteil vom 26.11.1963 VI ZR 221/62) which dates back to 1963 says that the employer needs to show general "good will" in issuing the work certificate.
It doesn't say that you are always entitled to get the best one though because another judgement says that the certificate needs to be the truth.
There are thousands of lawsuits every year because of that. In the end the employer needs to bring up solid proof for wrongdoing to justify a bad certificate. So usually, if you get an job applicant with a bad work certificate, you can be sure that he REALLY messed up on his last job. Unusually it would probably be better for the applicant to say he/she has been unemployed than show up with a bad certificate.
It doesn't say that you are always entitled to get the best one though because another judgement says that the certificate needs to be the truth.
There are thousands of lawsuits every year because of that. In the end the employer needs to bring up solid proof for wrongdoing to justify a bad certificate. So usually, if you get an job applicant with a bad work certificate, you can be sure that he REALLY messed up on his last job. Unusually it would probably be better for the applicant to say he/she has been unemployed than show up with a bad certificate.