How to sell a map and create a retail web site

This is a very clever business web site. Kudos to this Colorado business. They sell trail maps and books for outdoor activity. All very well, but what's clever is their combination of service and marketing. For example, the Minnesota Bicycle Trails Reference Map costs $5.00 or so. The site lists every trail on the map with supplemental information. So how does this help them sell the map? Each trail profile is followed by links to the maps and/or books that reference the trail. No mapping information is included.

So they combine value delivered for free with marketing, and intelligently link the products to the marketing. They also have an affiliate program for others who wish to set up store fronts.

This is the way web marketing and advertising ought to be done. Why can't others figure this out, darn it?!