When you say 'models', do you mean people you've actually hired to photograph? Because that's what 'model' means. If so, they have at the very least verbally consented and the proof that they have consented is in the picture - the fact that they have posed for your camera. The only case they have against you is "HE MADE ME LOOK UGLY!!!", which admittedly, is a very timely problem for photographers, but definitely still recognised as nonsense by lawyers ... as of 2013.
If you're talking about 'candid' photographs in the street, completely different story. And in which case, who are you selling the prints to? Galleries? Directly to other people? Regardless, assuming you aren't intentionally photographing subjects doing something criminal and assuming you aren't doing something criminal to get (or in distributing) the pictures, and assuming you haven't aggressively invaded people's personal space (to their distress illustrated in the picture, but this is still ambiguous in the court), nobody has a case against you. With that understood, 'selling prints' to the public or galleries puts the images safely in the realm of art. This is all common sense and I'm sure the law in Germany respects it.