Definitely recommend "try before you buy" - send short samples out and see whether their feedback works for you. And just because an editor has a big reputation doesn't mean to say they'll be good for you. Also, get an idea of price before-hand, and don't presume high fees means high-standard of work.
Indeed. I sent out a sample to an editor who came highly recommended (not a Chronner!) for my crime novel. When I received the sample back, she had been very thorough with her editing, but so much so that she'd pretty much rewritten the first 1,000 words in entirely her own style. She said, very magnanimously, that she'd be prepared to take me on as a client, but I declined. There wasn't a single positive comment, not even a hint of one, in her entire edit. Not one of the edits were for grammar/spelling/style as such, but she changed pretty much everything else. I have no objection to being torn apart, but the prospect of 90k words of negativity just blew my confidence in myself completely.
After her sample edit, I failed to write anything at all for several months. I completely lost my creativity until a certain Ms Zebedee took me to task over a coffee and made me think through why I'd lost it. We worked out between us that this editor had been the cause. I have since discovered that a) she's really picky about who she takes on (I'm really not flattered) and b) she has alienated many, many of my writing friends over the past few years with her acid tongue.
Now, I consider myself to have a fairly thick skin when it comes to critique, but I discovered that I have limits! When
@Teresa Edgerton edited a fantasy manuscript for me*, it was a totally different experience. She tore it apart with the greatest kindness, found plenty of positive to keep me inspired, and was in fact the best mentor/editor/friend I could possibly have had. Such a difference. I can't recommend Teresa highly enough.
Definitely send a sample before committing, and then think carefully about whether that editor's style suits you and your writing before you sign on the dotted line.
*Sorry, Teresa. That MS is still sitting partially edited. Since my Mum died, and I became sole carer for my father (91 with dementia), my writing slots have decreased to 20-30 minutes at a time most days. However, I have applied for an Arts Council grant to enable me to employ carers and pay for a couple of weekend retreats so I can have a concentrated effort to knock that story into shape. Then, I plan to submit it everywhere (carefully and in a controlled manner!
)