When should a writer finally admit that it's not your query that is the problem, but the subject matter?
I've written a YA suspense novel set in the 1960s. Those who have critiqued it with me think it should sell. However, I've sent out well over 100 queries, many following extensive revisions suggested by members of several writers forums. None of my queries have garnered even as much as a request for a partial. So, when should a writer give up and realize it's not the query but just something no agent or publisher wants?
Having not read the query or the novel, I can't tell you where the problem is. However, if you've sent out over 100 queries and not gotten a nibble, something is wrong.
When this happens and you really don't know if it's the topic or the query, set it aside. Hopefully you've been working on another novel during your submitting process. If not, get started right away on one. When it's done, start querying it.
Then do it over again with a third novel.
During the process, your writing will improve and you'll learn more about submitting and eventually you'll hit it right.