'Getting the right answer is only possible when you have asked the right questions.'
That is the pithy advice I just found in a fortune cookie and a more appropriate cookie aphorism could not have been written for a reference librarian. The principle of answering patron's questions is to first pepper them with more questions to get at the specifics of what they want to know. That is called the 'reference interview' in libraryland.
Patron: Do you have Kovel's Antiques & Collectibles Price List?
Librarian: Yes, we do; the latest edition is a reference copy, but you can take out the older editions. Is there some particular kind of antique you are researching?
Patron: Yes, I don't suppose what I want is in Kovel's anyway, because I don't want the price, I want to know what the mark means.
Librarian: We do have books of silver marks and china marks and so on. What kind of piece do you have?
The patron then went on to describe the piece and to tell me that she wanted similar pieces, but could not read the mark and did not know how to look up information about it. I set aside several books on china marks and identification and also suggested that she take a picture of her china for the antique dealer if she didn't want to carry it with her. If we had just stopped the conversation at the Kovel's guide, the patron may not have gotten the answer she needed. I hope she gets back to me about whether she was able to identify her china.