How do you purchase rare books?

I had a question from a graduate student over the weekend, and it got me to thinking as I tried to answer it. I'm just wondering if my experience is at all unique. The student asked "how do you select items for your collections?," in relation to an assignment that requires writing a rationale for the purchase of a rare book worth less than $5000. I answered the student, and an edited version of my response is below, because it occured to me that this would make an interesting blog post.

The answer to the question, in my case, is both simple and complicated. In my (somewhat limited) experience, most special collections librarians with collection development duties have a written policy, but that policy is rather broadly written, and there is a lot of latitude *within* that policy.
Mine can be found here for comparative purposes.

It may be just my own ignorance, but I don't know of any "best practices" standards in our profession as far as acquisitions go (as opposed to, say, transfers). My acquisitions criteria are radically different from those of say, the Newberry, because we focus on different types of materials. There are items that I actively pursue for our collections that the Newberry wouldn't touch, and vice-versa.

What that means, then, in real terms, is that the curator of a collection gets to put their personal "stamp" on it as they add to it. For instance, I'm responsible for a private press collection, and I've gone out of my way personally to purchase private press books by female book artists and book artists of color, because I saw that they were under-represented in that collection. I do the same thing with our children's books--I've mostly purchased books for girls, because they were under-represented in the collection in relation to their contemporary market.

When I buy a book, I consider a few things. Since my budget is limited, I tend to rotate which collections I purchase for from year to year. So one year, I'll focus on African-Americana, and another year, I'll focus on our Private Press Collection. I tend to keep a file of things that I've realized we should purchase at some point: either from faculty requests, or from suggestions, or from gaps I've noticed when putting together a class presentation or answering a reference question, for instance. Sometimes it's just a matter of something in a catalog catching my eye as a good fit for the collections. Sometimes I target specific dealers with whom I wish to build relationships. Those relationships sometimes lead to early quotes on materials that would fit well into my collections. Sometimes I just see something on a bookselling website that catches my eye while looking up other items.

I know that it sounds haphazard, but it's not quite. After nearly 5 years with my collections, I have a fairly good grasp on what we have, and what we need. When something "catches my eye," it's more that I've seen something that would fill a gap that I noticed and filed into the back of my brain (or written into a bibliography) or put on a list at a previous point.

In my case, I generally don't need to write rationales for my purchases. With my departmental budget, I'm trusted to do what's best for the collection. I've only had to write rationales for expensive purchases coming from a different collective library fund, and they nearly all sound something like: "this particular item [x] is an example of group of items [y], which is not yet represented in our collections. I would like to add it to our teaching collection so that students can see the continuum from [w-z], which it illustrates in these ways..."

I'm just curious if my experience is much different from that of other folks doing similar work...