Sure if you browse by github but in my use of the site over the years I go to the repo from the webpage of the project or from another source such as a link from a blog or something.
Yeah, I'd argue that the project can be good and not widely used. Do you think that there are projects with real use case and are great open source software and not widely used because its buried under the *s?
It could be a relatively inexpensive way for niche marketing. Especially if the developer has a payment option with the software. Probably a decent way to get the software out in the open for profitability, no?
From a pragmatic standpoint, yeah it would accomplish that goal. However, that discounts the intended purpose of the stars, which is to represent an individuals attribution of personal value and trust. They lose significance and become misleading if you can buy them, which holds true even for good software. When we see a github star is should represent someone who has used the software, finds value in it or who respects and trusts the project.
Just trying to play a little devils advocate. Not saying that its ethical to do it, but if morals/ethics don't play a part in the decision, it could prove useful. Besides, I'd imagine that its already being extorted pretty heavily if there's that much competition for sellers, hah.