Prices change frequently on just about everything you buy online. Some times it can happen several times a day.
Amazon and other online retailers often promise to pay you the price difference if the item you buy lowers in cost after you make the purchase, but most people don't track prices on things they've already bought.
Paribus is one app that helps. It scans your email for receipts and searches to see if the price for the item you purchased goes down.
The app's developer says it will automatically send an email to the merchant asking for the lower price and credit your bank account.
It also keeps track of shipping time, too.
"A lot of stores promise that your package is supposed to be in by Thursday, and it ends up getting in a little later, like Friday, Saturday, Sunday, Monday. Well, you can get the shipping costs back or if you're a (Amazon) Prime member — get an extra month of Prime," said Eric Glyman, of Paribus.
There are other plugins and apps like Honey, a handy service that will save you money, before you spend it. They let you know if the item you're about to buy is cheaper at another merchant.