I get the same "but I am an A-student at VastlySuperiortoThisU" in my face to face classes as well. They are genuinely surprised that my college course here at NEStateU is actually a real college course.
I dread having to deal with this in online format in two weeks...
This might be an opportunity for the "Yeah, so was I. What a surprise to find the high standards here, eh?" approach. Or, "Yes, when I was at IncrediblyElitePrivateU, I could expect much more than this from all my students. I'm glad to see you realize now that these standards aren't so tough, and look forward to seeing a great improvement from you."
For some reason, when I (deliberately) misunderstand the implicit request to grade them more gently, they eventually back off. It might work for you. Good luck.
Oooh, I'm stealing this idea, Conjugate. I had been just flat out saying, "This course has to transfer to Flagship U and Neighboring State Big U. Therefore, I grade you on the equivalent of what is required there. The benefit of taking the class here is that we have small enough classes that you can get personal attention by bringing your questions to class and asking during the small group work session or coming to student hours."
Of course, I have far fewer of those complaints than "Nobody could possibly do this work" for my third-grade-level inquiry activities that require arithmetic, but that's a different complaint.