Writing is a craft, and those who refuse to learn (and then think they can depend on editors to do the hard work for them) should NOT be surprised if their books do not fly off the shelves.
It is never our circumstances but our mindset that holds us back. Lack of funds has never held back the determined and dedicated writers that I know personally.
Style comes from a lot of writing + reading a lot of well-written books. As Rebecca pointed out, “Bad writing is not a style. Word choice and how a writer structures their prose is part of it.”
I think there should be transparency in such things. I don’t like to hear of newbies being scammed. Knowledge is power and should be shared. Fairness is important, and I would hope that, as a community, we value those who do a good job for us.
Strictly speaking, true betas are just casual readers, preferably your ideal reader (someone who enjoys the genre/subgenre that you’re writing in). Many will disappear, never to be seen again, if the story is not in an almost finished state.
A developmental editor should be able to give feedback just by looking at the first three chapters. They will be able to identify any lapse in logic, under-developed scenes and characters.