In that case, I suggest you complain to wherever it is you're seeing such misleading information. I regret having offended you. I've only encountered such listings on eBay, and eBay is a hopeless case.
I've never yet bought yarn online. My last mail-order of yarn (Mary Maxim, or Herrschners, or Annie's Attic?) was well before the internet came to be.
I'll point to Debbie Bliss Cashmerino yarn as an example. Given the name of the yarn, one would assume that Cashmere would be the major fiber but that is obviously not the case. The fiber content of this yarn is 55% Merino Wool/33% Acrylic/12% Cashmere. This is how the yarn is marketed on sites which sell yarns, I'm not talking about eBay. Other yarns with Alpaca in the name often contain as little as 5% Alpaca fiber.