Given that we're situated in a college town, many students come to our store to buy their books rather than waste their life standing in the interminable check-out line at the University bookstore (doesn't matter if you have them pull your books for you ahead of time, you still have to wait in line approximately one hour if you wait to buy your books after 9am on the first day of term). So I have learned to ask customers if they have a preference in translation; it does avoid hassle later on when a student learns they've purchased the very pretty Penguin Deluxe edition of Swann's Way, translated by Lydia Davis, when they really need the Moncrieff-Kilmartin translation. Trust me, that can turn into a serious problem on the sales floor (i.e. tears). I also have a tendency to quiz the heck out of students when they have no idea which translation is needed; if they're bound and determined to buy a copy right then and there I'm going to try and figure out which translation they'll need. In a related customer service quest, I have also seriously confused a customer by asking if they needed a Spanish or English edition of 100 Years of Solitude (Marquez does crop up frequently in Spanish-language literature courses in the original).
Why is the issue of translation so important? Why is it so important to me and why should I care? Well, in the most superficial instance, it's an attempt to provide good customer service. I can specifially search for the Lattimore translation of The Odyssey to see if a copy is on hand rather than just dragging the customer over to the poetry section to have a rummage through the shelves only to find *oopsie* we just don't have one in stock and dragging said customer back to the desk to order one. Also, if the customer is really looking for a book in the original language I need to know before we head to the shelves; we have Death in Venice in a couple of different translations but Der Tod in Venedig has to be ordered from the warehouse (I don't have quite this problem with newer literature - the copyrights are still in place so there's usually just one, maybe two, translations available for authors like Saramago, Kundera, and Murakami).
The more in-depth reason is that I would like the customer/reader (and by extension the recipient/reader, if the book is a gift) to read and like the book that is purchased. Very few people have the capacity to read fluently in multiple languages so readbility is key, particularly when reading for pleasure (I read very differently when reading for pleasure as opposed to class/bookclub). Some translations just aren't that fun to read. Mandelbaum's translation of The Inferno is regarded as one of the most literal while not so poetic; on the other hand, Ciardi's translation of The Inferno does play a little fast and loose with "literal" translation but flows quite well. Garnett translations of Russian authors like Dostoevsky, Chekhov, and Tolstoy are the most common and widely available editions, being the first English translations of those works and, for the most part, in the public domain; however, Garnett occasionally omitted phrases or passages of the original Russian she didn't understand so the reader may be missing nuances in the writing. A student may need an inexpensive Garnett translation of Anna Karenina for school but I would recommend the Pevear and Volokhonsky translation to read for pleasure. Similarly, a prose translation of The Iliad might be cheap but a lyric translation evokes an ancient blind storyteller, sitting near a fire:
Rage — Goddess, sing the rage of Peleus’ son Achilles,I would love it if a customer responded to my translation question with "I really hadn't thought about it" or "Not particularly" that way (a) if they didn't know which translation was necessary and didn't want to seem gauche that's a good cover and (b) if they really didn't care and would like me to help them choose it's a good way to get a conversation going. I do really like to talk to customers about their reading (not about their Grandson Jimmy's dog's fleas or their husband's up-coming colon surgery, in detail). Having an actual conversation can be a rare thing but it's far preferrable to my last encounter with the translation issue; the student I was helping rolled her eyes when I asked about a translation and slurred "Like, American? duh?" Gah!
murderous, doomed, that cost the Achaeans countless losses,
hurling down to the House of Death so many sturdy souls,
great fighters’ souls, but made their bodies carrion,
feasts for the dogs and birds,
and the will of Zeus was moving toward its end.
~Robert Fagles, 1996
(Incidentally, if you like The Inferno check out the translation edited by Daniel Halpern - 20 contemporary poets translated/interpreted the 34 cantos. It's really fun to read.)