It seems like most people are arguing the side of the "LFS's fault" or the "customer's fault" when really the answer should be both. Yes, your local fish store should be knowledgeable, should give you sound advise and shouldn't be in it to make a quick buck, but it is also the customers responsibility to do research both before and as a follow up to the advise given at a LFS.
I compare the way I feel about my fish to the way some people care about their dogs. Real "dog people" don't just go to a pet store point and say "I want that one." The figure out what type of dog they want based on care, personality and what would be the best fit for their family. Really, the unfortunate part is that the saltwater aquarium hobby is one based on visual appearance and so people are more inclined to walk into a LFS and do the point "I want that one". If we as customers treated saltwater aquarium livestock with more respect we would do at least some research before hand, wanting to know what fish, inverts, corals would be best for our "home". Rather than walking into a LFS, looking at what came in that week and picking something. Why not be patient and wait until they have what you want based on your research? Or even ask if the LFS could add what you are looking for into their next order for you.
All that being said I do also agree that your LFS should be knowledgeable about what they are selling and be able to give a customer sound advise regarding their individual situation. A LFS, when approached with a question, should, as some have pointed out, ask about your individual situation and be able to give you possible solutions to your problem. If they can not, I still don't think you can hold it against them. If they give you outright wrong advise, that's when it is their fault. I think someone brought up going to the doctor as an example. Doctors can't always pinpoint what is wrong with you based on what you tell them and even some simple tests, they may need to run other tests which involve other people helping them to help you.
I may have started to ramble, I do that, but to sum up:
1.) Customers should do research out of respect to the fish, inverts, corals they are keeping and those they wish to keep in the future.
2.) LFS should be knowledgeable about what they are selling, but we can't expect ANYONE to know every little detail about everything, especially in such an extensive and diverse hobby.
3.) False knowledge and bad advise can and will happen and that is the fault of whoever gives out that advise, but not completely. There should be at least some fault on those that take advise blindly.