When I logged onto Amazon.com to check out the new releases in business books, this headline jumped off the page: Real Estate Sale: Save up to 39%.

The headline was followed by this: Whether you're a real estate professional or a first-time home buyer, find all the guides you'll need for becoming a landlord, finding a mortgage, selling properties, and investing in one of the most time-tested and popular strategies for building wealth, all at up to 39% off for a limited time.

Among the deals:

• Flipping Properties: Generate Instant Cash Profits in Real Estate, which is 33% off.
• How to Be a Quick-Turn Real Estate Millionaire, which is 35% off.
• Investing in Duplexes, Triplexes, and Quads, which is 35% off.
• Why We Want You to Be Rich, which is 37% off (this book would be a ripoff at 99% off, in my opinion).

Granted, most books are on sale at Amazon (NASDAQ:AMZN). That's why I love it. But it does seem a bit unusual that they're advertising especially deep discounts on real estate books. One possible conclusion: people aren't buying them. If we go with the theory that the bull market in real estate was in fact a speculative bubble, this makes sense.