I get a lot of questions about the "market value" listings on the Collectible Book Vault so I figured a peek under the hood for transparency benefits all. This project began for me when I had to attach value to my own collection for my insurance company. To them a book was a book. To me that line of thought was blasphemy. Books are sacred objects of art;) There is no regulated authority for pricing and attaching value to books other than "current market value". So I decided to keep track of the books that had the most value in my collection at that point. I decided to collect all publicly available disclosed confirmed sales prices. This is mostly Ebay and Facebook but also some auction houses (like Heritage). Abebooks has no historic sold data afaik so I can not track books there. Many collectors from our small community also privately share their sales and acquisitions with me. Those are always used with discretion and stored anonymously (only price and date). I only use this data from directly involved parties, either the buyer, seller or both. This is especially invaluable for rare books which often changes hands privately. The prices I enter in the database are always the prices that the buyer pays for the book. So ebay and auction house fees are included in this. I used to deduct 15% from Ebay sales but reversed that practice. My reasoning is that value is best represented by what a buyer is willing to pay and that includes auction house fees. I don't add shipping, sales tax, VAT or import taxes separately since they vary too much internationally. Sometimes shipping is included in a sales price, which I see as a service of the seller and not detrimental to the value of a book. For data shown on CBV I always use the median for the last 5 recorded sales to minimize the influence of outliers. I soon noticed this is a bit problematic for very rare books which only change hands a few times a year. For those books I choose the median of the last 3 sales. By using the median the visibility of fast up- or downtrends also lag behind. Since my main focus is long term value, this bothers me less, but to accommodate the community I also show the last recorded sale so interested parties can draw their own conclusions with a bit of their own research. A popular request is to show number of sales on which the value is based. The short answer is: the most recent 5 or less. I have data going back into 2020 but I am saving those for future projects where I will track values year over year. The book with most data points is Exorcist AE by Suntup Editions with 91 datapoints over 2021. But a book like Dune from Centipede Press already accumulated 30 datapoints in 2 months! Some are so rare I have not been able to record a single datapoint, like deluxe Nosferatu by Centipede Press. So basicly when you see a market value you are guaranteed it's based on the most recent sales: minimum of 1 and maximum of 5. I believe a disclaimer when a value is based on less than 3 sales would be a good addition and something I will most likely add in the near future. I also implore all readers and users of CBV to notify me when you see something that's odd or wrong. I am human after all and prone to error with databases that become larger and larger. With your help I can finetune to perfection ;) Stay healthy and keep reading. Yours truly.