What is Reddit's opinion of A Guide Book of United States Paper Money 7th Edition?
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By popularity on Reddit, this product is:

#8 in Antiques & Collectibles Encyclopedias books

7 reviews of this product found across Reddit:

If you're interested, get yourself a copy of the Friedberg Catalog. It is THE Bible of US paper money. Don't get hung up over the prices, but do play close attention to the document itself.

Here's an inexpensive version, printed in color.

As the old saying goes, "Buy the book before you buy the note." In other words, pick up a reference guide (such as Friedberg for US paper money) to understand what you want and how much you should expect to pay for it.

Good luck. Some notes will be expensive, like the red seal $1. I’d recommend getting a copy of this book to help you out, or this one.

Friedberg's US Paper Money is considered a good resource, though prices vary over time and the market is hot right now. In addition to seeing auction prices (sold prices, not just listed for stupid prices) on ebay, heritage, etc. should give you a good idea of value. Serial numbers not so much as far as additional value, unless they are fancy, in which case could add a premium.