Shading error after importing

Question

I am doing a project with some buddies for university and we all work with different Programms and decided to reder the final project in blender, but I am having major shading problems with their 3ds max and cinema 4d imports.

This is how it looks like with flat shading and I am particulary looking at the thrusters and the Cockpit. And when I turn on smooth shading it looks like this: Be aware that there is an edge split on in the last one. But evern if i turn that off it just loks much worse. The view on the cockpit etc. has these weird shading that almost looks like a few of the verticies are flipped.

For your Information, the whole object has only a single greyish diffuse material on all of it, no glossy or anything. All the faces are looking in the same correct direction. I am having this problem in many many other files aswell so if you need more information let me know.

Thanks in advance for answers. Best regards.