Price guides for what? Baseball cards? Records? Comic Books?
When I was a teenage comic book geek the Overstreet Comic Book Price Guide was my Bible, but over the years I quickly learned that market trends change so quickly (not just in comic books, but in any sort of collectible) that by the time a book like that sees print, it's already out of date.
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"If you're a false, don't entry, because you'll be burned and died!"