Do not go unarmed into the dark.
Now let's consider something quite different. This is a book that is not available online today but will be. Howes has it as an AA so it's bound to come up. It's Theodore Roosevelt's first book, The Naval War of 1812; or, The History of the United States Navy during the last war with Great Britain. This book was of no significant value until recently when, in 2006, it twice sold at auction for more than $1,000. It is now going higher. It seems to rarely reappear in catalogues once offered. It simply sells. If you are pricing this book it feels like it might be $1,500 and if an exceptional copy perhaps more. In the AED the average current estimate is $365.79 but a very good copy for that price is going to be a lucky find. In this case higher recent prices trump older [and] lower realizations. Markets change and Teddy is once again charging up the hill. AE Footnote
Typically when values noticeably increase higher prices bring out other copies. On the listings sites today there are no copies of the 1882 first edition to be found. This will of course change but the upward tilt in valuation looks encouraging to sellers and interesting to buyers.
Finally let's look for copies of Gone with the Wind. When it was published perhaps 15% of all American households obtained a copy. Copies are not rare. On Abe a search with the title in quotes finds 5,090 examples so we'll focus on the first year published  and signed copies and still find 39 examples. This is a relatively common book that still brings big money but how much is it really worth?
Based on records in the AED from 1961 to the present this book has been steadily increasing in value. Auction valuations recently reached $10,000 while the average adjusted current valuation in the AED is about $4,500. On AE the search is Gone with the Wind signed first [AE Footnote]. On Abe there are a dozen copies that fit the "first and signed" criterion. Four of them are priced under $10,000 and eight above. There is also an association copy offered by James Pepper that is signed by the author and has, laid in, a letter from Clark Gable about his role in the film. This copy is $85,000.
While the AE valuations are low relative to today's asking prices they suggest that looking past the asking prices to the transaction history and the frequency of appearance at auction immediately enhances a buyer's perspective and brings some realism into the purchase discussions. It is easy to look on listing sites for guidance about pricing but the real story is always going to be in the transaction history. That's what collectors paid and its good evidence of what they will pay.