Choosing Review Quotes

I'm still at a loss about how to choose quotes from a review. I can't find any guides about doing this. I'm not sure what level of editing is considered ethical (some reviews have single words they've picked out, but without seeing the original, I don't know why they did that). I don't know exactly what changes need to be marked and what doesn't (I found at least one quote I think changed the capitalisation without noting it). I don't know what part would most interest a reader.

So if anyone has any thoughts, knows of any articles, or otherwise has advice, it'd be welcome. I realise other people don't seem to have an issue, hence the lack of advice articles, but it doesn't change the fact I could really use some help. I mean, I understand how to pull, "This book is wonderful!" or the more ironic, "Worse book of the year!" But not how to choose a quote from an average review. It's all just word soup to me.

I can't pick one short positive sentence because the review doesn't have one. The style tends towards longer sentences, which may contain good and bad in them, in multiple pieces like this sentence, so if you put that in a review quote reader's eyes would be glazing before they got to the part I'd actually like them to read. It's the trimming that's the issue.

My issue was really that how I lifted the phrases could easily be a lie by omission in this case. I don't like quoting a positive part of a sentence if there's a negative in the rest. I realise publishers do stuff like that all the time, but I'm not comfortable with that.

I guess my main issue was weighting up whether the discomfort was something I needed to get over or whether I should pick a less useful but comfortable quote. I've had comments all over the spectrum from it's fair game as long as they said it to including the whole sentence or nothing.

I did pick something based on responses. Given they were so wide ranging, I went with my feelings and picked sentences that didn't mix praise and criticism. It might be the poorer marketing choice, but it's the choice I can live with. We'll see how it goes. Maybe no one reads that bit of the product page anyway and I'm worrying over nothing.

Thank you for the responses, as talking about it did help me figure things out.