As a dabbler in online booksales, I can’t say Amazon.com’s recent stumble is a surprise.

Four years ago, when people thought books ( new or used ) online, they thought ABE, Amazon or Alibris. Now there’s a dozen new and used book exchanges. Good news for buyers, and a great opportunity for sellers who spread their listings across multiple exchanges. However, the shift in the marketplace means something else for the individual sites: less buyers.

Better luck next quarter, Amazon.com.