Bliss, I agree with you that Lucifer is his own spirit and not part of the Goetia. That part is true. But saying he would never let a demon reject a magician’s call just because someone is using black magick or rebelling against dogma is your personal interpretation, not a rule.
The original question asked if a bad relationship with Lucifer would stop Goetia spirits from working with someone. The answer is yes, it is still possible to work with Goetic spirits even if your connection with Lucifer is poor or nonexistent. These spirits are not under his command. They are not his subordinates. Many have their own ancient origins and alliances.
Also, you do not need to seriously offend a demon for them to ignore you. A spirit might decline for many reasons that have nothing to do with offense, like poor timing, incompatible energy, unclear intent, or being blocked by another force. Rejection does not always mean insult.
Zepar being patient with you is a good example of how spirits can be understanding, but that experience doesn’t mean others will act the same way with every magician. Each connection is unique.
So to be clear, yes, you can work with Goetic demons without a strong connection to Lucifer. They choose who they work with based on the individual, not because of their loyalty to Lucifer.