There are two classes of merchant on Amazon.com: those who get special protection from counterfeiters and those who don’t. The first category includes sellers of some big-name brands, such as Adidas, Apple and even Amazon itself. They benefit from digital fortifications that prevent unauthorised sellers from listing certain products for sale. Many lesser-known brands belong to the second group and have no such shield. A popular cat toy called the Ripple Rug, invented by Fred Ruckel, is one of those brands. A few months ago, knock-off merchants based in China began selling versions of his product, siphoning off tens of…