My sister is a tattoo artist, she too has engendered quite the instagram following posting her work, which draws clients into the shop.
People participating in these sorts of communities enjoy the fact that nobody's clubbing them over the head with a 'buy' button, and because of that the level of engagement is much higher than it is on a site like Etsy, for instance.
Instagrammers follow somebody for a few weeks or months, and when they're ready to buy, they make an inquiry, and by that point they're willing to go to any length to get their hands on the product. It's the diametric opposite of impulse buying. The ongoing and intimate narrative is essential to cultivating this, and the absence of a buy button makes it a very inviting place for the types who are into that sort of thing.
Isn't this just because Instagram makes impulse buying nearly impossible? To make a sale on Instagram, you have to cultivate a serious following who will go to great lengths to buy from you, because it's so hard to buy anything from an Instagrammer.
Upvoted nonetheless, because those examples of how people find business opportunities through Instagram are great.
You also have to ask where does the buying cycle and Instagram intersect: http://www.forentrepreneurs.com/buying-cycle-and-triggers/
The reality is that the ecosystem just isn't there to fully support cost per acquisition based transactions (the name for what your suggesting) in a way that satisfies provider (like Instagram), Brands (like Nike), Platforms (Like amazon, etsy), and Payment processors (this list is huge).