Rae Armantrout today said that, in her opinion, there are only two reasons to write a negative review of a book of poetry:
1) The book or the writer has been majorly built up and praised by lots of critics and/or poetry communities in general and you want to to take said author down a notch. You want to reevaluate the author and show how perhaps they are not quite everything they are being made out to be.
2) The book or writer you are reviewing is indicative or representative of a trend or a school within poetry that you are against and want to position yourself against.
But she advised it wasn't worth it to write and publish a bad review of a book by a not-so-well known author who is not representative of some trend or school you are against. In her view, the attention given to poetry is miniscule enough that there is no reason to bash someone who might have very few other reviews or very little response to their work. If you like the work, you can review it and help to draw attention to it. If you don't like it (and it doesn't fit one of the two categories), review something else.
I think her recommendations seem smart. I also think these same guidelines would work within the translation mini-world as well. No reason to bash a translator's work, especially when said translator is low- or no-paid and who likely receives little appreciation, respect or substantive response to her work. Otherwise, bashing the translator or the poet doesn't seem worth one's time. Unless one is petty, small-minded or just cruel.
Just sayin'.