This is a guest post from J.D. Roth, who writes about personal finance and related topics at Get Rich Slowly.

Back in our young and foolish days, my wife and I bought a set of encyclopedias from a door-to-door salesman. This was in 1995, at the very cusp of the digital age. We had been on the internet for about a year, but we had no way to know that one day very soon the World Wide Web might make printed encyclopedias obsolete.

So we bought an encyclopedia set. Naturally I charged the $500 to my credit card.

We used the encyclopedia for several years. Then in 1999 we discovered Google. The encyclopedias began to gather dust.

Even so, when we moved to a new house in 2004, we took the books with us. We installed them prominently in the living room, but we never used them. Eventually we moved them to storage. For the past two years, we’ve tried to sell them at our neighborhood garage sale. The first year, we priced them at $50. This year we priced them at $20. Nobody wanted them.

On the last day of this year’s sale, a man stopped by and sorted through our book collection. He was rather particular about his selections, so I struck up a conversation with him. (Bibliophiles are happy to meet kindred souls.) He told me he owned a used book store. “You’ve got some good stuff here,” he said, patting his stack of books.

“Thanks,” I said.

He turned to leave, but then paused. “You know,” he said. “These encyclopedias are worthless. I have a dozen sets in my store. They used to sell pretty regularly, but nowadays I can’t even give them away.” He waved good-bye and left.

It hurt to think that our $500 set of encyclopedias was worthless, but I had to admit it was true. I put them up for free on Craigslist.

The next day a man stopped by to pick them up. He was ecstatic to find them. “We don’t have a computer,” he said. “And my daughter is in the fifth grade. She loves to learn. She’ll use these all the time. Thank you.”

I helped him load the books into his car, a mid-80s Honda Accord. The rear of the vehicle sagged beneath the weight. Before he left, he fished out his wallet. “Do you have a Blockbuster Video around here?” he asked. I said that we did. “Here,” he said, handing me a Blockbuster gift card. “Take this. I mean it. You don’t know how much I appreciate this.” I thanked him and took the card, which I tucked in my wallet and then forgot.

A few weeks ago, I found the Blockbuster gift card. “I wonder how much credit is on this?” I said to myself, scanning the fine print. I tried to call the toll-free number, and to check the web site, but neither would give me the balance. To obtain the balance on a Blockbuster card, you have to actually go to the store. So I did.

The card had $16.50 on it. I thought maybe I could pay for part of a game for my Nintendo Wii, but nothing looked appealing. I scoured the DVDs, but couldn’t find anything I wanted. At last I spied The Godfather. Aha! Hadn’t I been wanting to purchase that for a long time? It’s been three or four years since I last watched it. I bought The Godfather and a pack of Red Vines and headed home.

But when I went to put the DVD away, I was dismayed to find that I already owned a copy. When did I buy it? Why hadn’t I remembered purchasing it? I considered giving the new copy as a gift to somebody, but then I recalled Cady’s guest entry at Get Rich Slowly about how to use the Amazon Marketplace for fun and profit. Taking inspiration, I listed the movie for sale.

The Godfather sold last night for $7.02. After fees are settled, I will have netted $7.16.

And that, my friends, is how I managed to turn $500 worth of encyclopedias into $7.16 in Amazon credit. That is personal finance at its finest.

There’s no real moral to this story. Each of us makes the best financial choices we can. But sometimes our information is imperfect. Sometimes we don’t know what the future holds, and sometimes what we think is smart (charging encyclopedias to a credit card) is actually pretty darn stupid.

Image credit: –Mandie–

You can find more of J.D. Roth’s writing about personal finance and related topics at Get Rich Slowly.