Most writers brave enough to give their work to somebody else and ask for comments have a vague idea of what's coming back. The depth of the comments and feedback will always depend on the experience of the person you asked to dissect your precious child and, intellectually at least, you are prepared to get back comments and suggestions that feel as though somebody has ripped out several of your internal organs.
Then you read them again the next day, and the pain is (usually) less, and you see which comments you agree with, which ones you don't, and you send back a nice note to the friend who ripped out you heart, thanking them for their help and maybe asking for a clarification or two. Sometimes they are painful, but they are necessary and we learn to take them in the spirit they are intended.
Then there are the writers who ask you for comments, but who are really looking for a mutual back-patting society, where everyody tells them how talented they are and that they are bound to sell this one because its so ground break/innovative/etc/etc. Its often branded as 'being supportive'. I guess it has its place. But then, people can be supportive and honest.
A quick aside, here, to establish my bona fides. I am an active member of the BSFA's 'Orbit' community of mutual critiquers, and I am the co-ordinator for Orbit-4. So I'm used to being on both ends of crits, on a regular basis.
I had a situation recently where somebody was asking for people to look at a published book and comment. I thought that was a bit odd. You normally ask that sort of question before publication. Now, to make this easier to write, I'm going to say this person was a lady, but she may not have been, in the sense of preserving anonymity.
So I read the free bit from the Amazon page, and while I was there had a look at the comments. The sample looked as though it had not had the benefit of a professional editor, the publisher was not one I had ever heard of, and the eleven 5* reviews all consisting of two words, like 'good read' and 'excellent book'. I pointed out how fake that looked (in the kindest way), asked about the editor, and made a few fairly gentle comments about things I saw as potential issues with the book.
Not a word back, not even a thank you. And I guess that's OK if you think what some authors have vented into the cybersphere when they've had negative comments made. Still, its made me think twice now about extending a 'helping hand' in the future. I guess the moral is be sure what you ask for is what you really want. And even if what you get back isn't what you expected, at least say thanks.