Editing is subjective, especially if you’re writing a book. Good grammar doesn’t necessarily translate to good writing, and in things like fiction a lot of liberties can be taken with sentence structure. English is a vast language that adopts from many others, and while it has some narrow grammar rules, it leaves the door open for interpretation and different approaches. Some of the best stories would be marked poorly by an English professor.
This is why samples are a very powerful tool when searching for an editor. At the end of the day, your editor is someone who needs to match well with your voice and your preferences. Samples show this, and they allow you to weed out editors who are maybe too heavy-handed or perhaps too light with the red pen.
Different results just mean you can pick an editor who is most aligned with what you’re looking for. It doesn’t mean these editors are wrong, just that they have a different idea of what the best approach is.