Some people are wiling to pay more for products than others. Because they are more or less wealthy, or simply because the product is more valuable to them subjectively.
When you put a product for sale on the internet, you don't know how much people are willing to pay for it and therefore you may be losing money. Because if you put a product for sale for 20,00$, 100 people will buy it. But if you lower the price to 15,00$, 500 people may buy it. 5.500,00$ is the difference.
The solution: an app that allows you to insert the price you are willing to pay for the product and that will send you an e-mail if the seller is willing to go along.
This will facilitate price formation among the sellers, will allow them to sell more for differentiated prices to each customer, and everybody will be happier by paying the price they think the product deserves.