Budget and time frame are two very concrete things to negotiate when looking for an editor. You know when you need the manuscript back and how much you can afford. But how do you figure out if your editor is suited to you? Do you need to take a Meyers-Briggs test and compare astrological charts? No, thank god.
Genre
Make sure your editor enjoys or has experience in the genre in which you are writing. I’ve had people tell me my memoir should be a novel (I don’t write novels) and my fiction-writing spouse has had people tell him short stories should be essays (he does not write essays). You want an editor who will meet you where you are and who will be enthusiastic and knowledgeable about your genre of choice.
Communication style
Does your editor respond to your emails in a time frame that works for you? Do you want to talk to the editor on the phone or by video call? Does your editor do that? Does the way they talk about their work make sense to you?
Feedback style
An editor is going to give you criticism, probably a lot of it. What do you need when you receive feedback? Do you want the unvarnished truth? Or do you prefer your criticism presented in a gentler approach? Do you need a lot of encouragement or reassurance?
None of these styles are right or wrong, unless you are an experienced writer and your editor explains each change she makes in excruciating detail. That is a waste of time for both of you.
Not sure what kind of writer you are? How do you respond to criticism or feedback at your job? How do you give criticism or feedback to other people?
How do you know if an editor is right for you?
Ellen Goldstein 
At my first university, back in the UK, there was a sign in the writing centre which read, “Please do not offer unsolicited criticism, as a smack in the mouth often offends.”
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That’s good advice! One of my online editing groups has an ongoing thread about the struggle between correcting mistakes and having friends, and I was shocked by the number of people who correct errors in their friends’ emails, etc. (when not asked or being paid to do so).
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I have to admit to struggling with some e-mails. I have a regular corespondent who couldn’t use their, there, or they’re appropriately to save a life. My teeth grind together whenever I read their messages.
Another friend routinely mistakes one word for another. Famously, the words “flamboyant” and “flatulent” were once mistaken for each other. The family joke is now to be a little flatulent in behaviour, or with money we haven’t got.
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It’s true. I have a friend who says “I” instead of “me” all the time, and it drives me crazy.
I mean, one could fart away money. It makes some sense.
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What he actually said was, “I’d like to have enough money to have my own little plane. I could fly to Paris for the weekend, be a little flatulent and indulge in the coffee-house lifestyle.”
Dead silence followed. Tentatively I asked, “Are you sure you mean flatulent?”
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And was your comment met with humor or offense?
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The friendship I have with that man goes beyond brotherhood, I don’t think it would be possible offend each other.
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Oh, if he’s your friend, then it’s just endless humor. (Humour. Whatever.) You can tease him about it until the end of time. Win/win.
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