First of all, we all make mistakes. No human can avoid it.
Second, all writers do their damnedest to produce a quality product.
Third, it doesn't matter how many people you hire or who volunteer to proof your work, invariable one little type slips by, which takes us back to the first point.
I belong to a few readers groups and forums (the other people are well aware that I am a writer), and I do read a few reviews sometimes to determine whether I want to download a particular book. There seems to be a disturbing trend for readers to grade a book they've read, and I don't mean on the writer's storytelling skills, but their grammar and spelling.
The majority of these type of readers used to be English instructors, but there are two other types I've noticed that are on the rise. One type are people who want to be writers. The other type are ones that want to sell you services.
How do you tell the various types?
The English instructors come right out and tell you who they are. For example, they have a beef because your sentences are fragments, even though your story is written in first person with a protagonist who's drugged or injured. Or a teenager must speak in perfect sentences. Or they taught with Strunk & White while you prefer the Chicago Manual of Style. But they generally feel they must save the universe from your alleged bad writing (which consists of one "from", accidentally spelled "form").
The folks who want to be writers like to jump on indies because there's nothing holding them back any longer from writing their Great American Novel. Paradoxical, I know, but their excuse for not writing for so long was the agent and trad publisher gatekeepers. Now, there's really nothing holding them back, but their own fear. They can't admit that fear so they lash out by complaining about other writers' style and/or typos. These people you can tell because they usually complain about your typos in a comment that is in itself full of typos.
I've seen writers try to elicit specific information from these two types of readers, only to be met with the response, "I'm not doing your work for you!" Frankly, these are perfect examples of why you leave reviews, whether on a private blog or a retailer's site, alone.
The third folk are fairly nice about your book's need for a major edit...until you ask them specifically what they found wrong. Then they equally nicely say they will tell you...for such-and-such fee. Solicitation shouldn't be on an unaffiliated blog or retailer site, but that's my personal opinion.
Once in a while though, you'll get a reader who nicely points out a problem and tells you what that problem is. For example, one of Alter Ego's fan sent her a lovely e-mail that said Chicago is on the shore of Lake Michigan, not Detroit.
We had a pleasant discussion about typos and how writers react to criticism. This reader was quite worried I'd be upset. I was actually more embarrassed than anything, especially since I named the correct lake for Detroit everywhere else is the novel. (It's Lake St, Clair, by the way!)
I thanked the reader profusely and sent her a corrected copy of the book and an Amazon gift card.
Does that mean you should send a detailed list of problems to every writer of every book you've read?
Not necessarily. It's one thing if it's an indie published book and you think the writer will respond civilly about a typo or three. (I wouldn't send a criticism of theme, style, etc. If you didn't like it, then it simply wasn't the story for you.) But for a trad published, there's is quite literally nothing the writer can do once their book is published.
On the other hand, don't send the writer a private e-mail saying, "Hey, you f***ed up!" without being a little more specific. Otherwise, that's just troll behavior, and it doesn't help anyone in the long run.