You might hire someone for a proofread, but let the editor know that you’re open to hearing from him or her if the work needs a heavier edit. The editor would need to present you with evidence in the form of sample pages that showcase what’s needed—and your job is to make sure you agree. You want to feel like an editor’s edits are polishing your work and making it shine. If you feel dread or anger, or even if you feel misunderstood, it’s likely not a good fit. At the very least you want to share your reactions with the editor so they can respond or change course.
Working with a professional is always the best choice, so if possible, then save up to work with an editor. But of course, some writers can't afford this, in which case there are some other options. You can barter with other writers in the same genre, editing each other's work, or providing other services you might be more skilled at e.g. Marketing tasks.
Hm, I’m a longtime freelance book editor and have a few thoughts to share. I think one page of editing is not enough to gauge much, and that you should be able to get a sample edit of 10 (double-spaced 12-point) pages from a potential editor. You’ll have a better idea after a complete chapter has been edited, and you should have a contract that allows either you or the editor to opt out cleanly at various stages. Another thought: sometimes authors don’t know what level of edit they need, and a good editor can assess this based on reading a few pages of your ms. and spot-checking the remainder. Also: a lot of book editors (like me) work primarily for publishers rather than for individuals. It’s just easier. I know I’ll get paid, I don’t need to educate publisher clients about the process itself, and they send me regular work, so we get to know each other’s needs and preferences. Lastly, I wouldn’t really expect a newcomer editor to be able to handle a booklength manuscript very well (I was that person once — eek). If it’s someone really new, they should have had good training somewhere imo. Book editing is a technical undertaking. It’s also about knowing what to leave alone. Inexperienced people often tamper with authors’ work unnecessarily. Anyhow, I’d be happy to answer any questions.
It’s always sensible to follow due diligence in submitting your first draft of your book to an editor by making as fool-proof a copy as possible for you because first, it is your own creation, and secondly, a horrid draft sent your editor can end up frustrating both you and him or her. Make your own corrections to the extent you can, so that will make the job of your editor that much lighter and the end result would be a lot more effective.