The next time your Instagram feeds up an ad, check the brand. Chances are, it's actually a third-party reseller using Insta's algorithm, content marketing and good-old-fashioned arbitrage to get you to buy cheap stuff.
At The Atlantic, Alexis Madrigal explains:
Some Instagram retailers are legit brands with employees and products. Others are simply middlemen for Chinese goods, built in bedrooms, and launched with no capital or inventory. All of them have been pulled into existence by the power of Instagram and Facebook ads combined with a suite of e-commerce tools based around Shopify.
This is a pretty typical method of selling online these days - middlemen selling products from Alibaba that get dropshipped by freelancers on UpWork - but the Instagram version has an interesting twist: Retailers can pay influencers to include product ads in their feeds. Since the whole point of influencers is that a lot of people follow them, retailers can get their product in front of literally millions of people.
From there, standard sales pressure tools apply: There's a (fake) countdown clock that urges people to buy now, tracking pixels that embed the same ad in other social media sites, popups indicating the number of (potentially fake) people who have purchased the product.
Or, as Madrigal puts it:
I like lions, so I follow an Instagram account that posts pictures of them, they post an ad, so I go to a webpage, and now I get ads chasing me all over the Internet advertising a lion bracelet. It's enough to make you long for the days of going to the mall or buying stuff out of a catalogue.