On the Amazon web site, as you look for a book (or any other item), they suggest you similar products. The put it as "readers who bought book Z also bought book Y", which at times seems very unlickely, but most suggestion certainly make sense.

As a buyer, you might also get email links suggesting a new book on a similar topic. Like a new Delphi or JavaScript book, or books on politics or business or architecture by the same other or related with books I bought. At times this is annoying, specifically when they suggest me to buy toys or electronics I cannot buy from Italy (but I got shipped to a US address while I was there), but this is another story.

Now for the second time a couple of weeks I got an email like the following (and I got a similar one forwarded by one of my readers):

We've noticed that customers who have purchased or rated books by Marco Cantu have also purchased A new geographical dictionary. Containing a full and accurate account of the several parts of the known world, ... Volume 1 of 2 by John Barrow. For this reason, you might like to know that A new geographical dictionary. Containing a full and accurate account of the several parts of the known world, ... Volume 1 of 2 is now available. 

The link refers to this book, now reprinted but originally published quite a few years back:  "London : printed for J. Coote, 1759-60". What this has to do with my Delphi books, I really have no idea. Even in case someone bought both at once, which seems odd, this should not set a trend... At the end of the message there is an ironic comment:

We hope you found this message to be useful...

It looks like something in Amazon system is really messed up!