I have been a Vinted seller for six months now and I have made just over £300 on the app so far.
The site allows anyone to sell their unwanted items for a price they decide and they can keep all of the profit. The company makes its money by taking a slice of the postage fee, something the buyer pays for.
Part of the simplistic beauty of the app is that as a seller, you don't have to deal with any of the addresses and now there are digital labels so no printing involved. Just bag up, pop in the post and wait for the money to clear.