I got burned by something like this. I hired an editor (not on Upwork) who had worked for a number of very famous authors (people you've heard of, people who've sold millions of copies). They did a fantastic sample edit, and the quality of the work dropped off precipitously by about the 20% point of the manuscript. The best-case scenario is that they just didn't care, because I'm a nobody and because of the novel's l…
I'm sorry about your experience.
But you might be interested in knowing that that phenomenon goes way back -- a lot of the "old masters" paintings were done by apprentice artists working under some level of supervision from the "named" painters. And I'm talking about really famous painters like Rembrandt or Reubens.
Also quite a few of the most prolific contemporary mass market authors have "assistants.