Editors come in all shapes and sizes. These days, you don't even have to meet them in person! I've edited several manuscripts for authors I have never met by utilizing Word, the Tracking Changes & Comments features, and email.
Before you hire an editor, or before you start researching what different publishing companies offer (in terms of editing services) make sure you know what type of editor you want/need.
A copyeditor usually just checks for grammar and spelling and prepares the manuscript so it is free of technical errors.
A developmental editor will read for content. They will help analyze the plot and characters (fiction) or make sure you proved your point (nonfiction).
Which type of editor do you need? Probably both.
A high quality editor may be able to provide all in one. The editor should be able to tell you what they can help you with, but it's best to ask a few questions and research their past work to get an idea of what they can do.
1. How many books have you edited?
2. What genres have you edited? Which are your strengths?
3. How many of those were published?
4. What sort of training/eduction have you received?
5. Do you do developmental editing and/or copyediting?
6. Do you know how to cite sources correctly (nonfiction)?
7. Do you think you are better at plot development or character development (fiction)?
It's also important to find an editor who is professional and will treat you with respect. You want an editor who will point out the flaws in your manuscript as well as point out what you did right. Be upfront and tell them what you want. This is your manuscript, so maintain control.
If you are ready to submit your manuscript to a publishing company, do some research. Do they have an editing department? What will the editing entail? What are the qualifications for hiring their editors? Do they provide developmental editing, copyediting, or both?
If you are accepted, see if you can talk to the editing manager (the one who hires editors and assigns them to projects) and request an editor with certain expertise or experience, if available. While editing is time consuming, finding the right editor for you will help your manuscript shine.