Most vendors, even larger ones do not have effective channel management or insight how to run an effective control over the market. The internet has skewed everything more towards B2C and most companies are struggling to adapt. I have seen so many bad channel ideas that hurt brands, hurt customers, and make everyone lose.
If a manufacturer has to resort to listing unauthorized dealers or sellers then their channel is broken, period. In most cases I have seen, these policies are created at the request of larger, legacy dealers who want to protect their higher margins and manufactures are afraid of losing the business.
When we first started selling B2B and security products online, we were told by many vendors that we were unauthorized, got swore at, and were told that end users could never understand the products and they shouldnt be sold direct. You would not believe the nasty calls we got from sales managers and reps.
Today 6 years later, we get invited to partner conferences, vendor events, marketing support, get listed as preffered places to purchases, and much better overall from vendors who know where the market is going. I have even been asked to give training calls to sales staff to show how to better manage a channel, pricing, and how to structure things that still allows integrator margin, while still allowing for online, retail and over omnichannel sales approaches.
We just got an email from an industrial supplier who is changing their name and whole business model from b2B only to b2b and B2c to compete now with amazon supply and others.
Specific to the question, if a manufacturer is trying to limit support to end users or resellers who want to sell the product, then they are not going to last long in the market. There are too many choices, and its too easy to access products now for this 1970's customer support doctrine.