The Silent Salesmen Too price guide is a useful tool but is often misunderstood. The purpose of this article is to tell you how the price guide was (and still is) put together, the assumptions inherent in the assigned values, and the limitations of the guide. In other words, what is the price guide, and what is it not?
Bill Enes put together the first price guides for Silent Salesmen and Silent Salesmen Too. Since Bill's death in 1999, updates to the guide have been managed by people who were close to Bill and want to see the guide remain current. The guide is copyrighted and the copyright is held by Bill's estate, so his widow has the ultimate say in when and how subsequent versions are written.
I don't know how Bill derived his prices, but I know that he had a "pricing committee" that at the very least advised him. I don't know how much of the advice he took, but it's safe to say that Bill's opinion weighed heavily in the final valuation.
Since Bill's death the price guide has been updated twice as of October 2008. As I write this, the latest version is the 2002 price guide, which was published in November of 2002. It's obviously outdated by now. The 2 price guides published since Bill's death have been collated by David Cook (in 2001) and Mary Zerby (in 2002). David Cook is an advanced collector of antique vending machines, old gum, and vintage gum-related advertising. Mary Zerby is the mother of Bill's widow, Peggy. Both of them have identified 16 to 18 collectors of old vending machines who they believe to be knowledgable about current prices. They've sent them the old price guide and asked them to carefully consider prices for the machines listed in the price guide and to change any price they believe is no longer valid. During this process there were several "ground rules" to follow, which I'll list here:
The meaning of "average value" can vary, so it's important to know how the average was calculated. In 2001, for each machine the highest and lowest valuations were excluded, and the arithmetic mean of the remaining values was calculated (in statistical jargon, tthis is a "trimmed mean") and then rounded up to the next reasonable increment. I don't know the exact procedure used to calculate values in 2002, but I suspect that the arithmetic mean was calculated and then rounded to a reasonable increment.
In my opinion the best and most complete analysis would be the following: For each machine, trim the top estimate and the bottom estimate, and report the median value and the range of values in the remaining set of numbers. From a statistical standpoint taking the median of a trimmed data set is redundant, but trimming the high and low values from the range would omit outliers caused by a single collector who loves or hates the machine beyond reason and whose lust or hatred unduly influences his or her opinion of the value. The current price guide format doesn't allow the range to be reported, but there's no reason the median couldn't replace the arithmetic mean.
This method produces a price guide based on a consensus of 16 to 18 active collectors, each contributing independently to an objective calculation of collective value. This produces a useful tool that's invaluable to new collectors and is often consulted by experienced collectors.
Having said that, the price guide is just that: A guide. It does not define the price, it just gets you into the right ballpark.
Some limitations are the following:
In general, machines tend to sell for more than book value rather than less than book value. I've not figured out why that is, but I've seen it countless times. I've seen superlative examples sell for 3 or 4 times book, although a superlative example obviously isn't one in average condition. The ultimate question on any purchase is "What's it worth to me?" The answer to that question may make you pay 3 times the going rate or to walk away from a bargain. In the end, you have only yourself to answer to.
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