When conditions are just right, you might be able to get your deposit back from the electric or water company. Some time back, I needed some extra cash. I called the electric company and asked about getting my deposit refunded. Because my account had been consistently paid in full and on time for however many years that company required, they sent me a check.
Paribus monitors the prices of things you purchase online. If the price goes down after you buy it, they ask the merchant to refund you the difference, all without any input from you. I had signed up for this ages ago, and when it stopped working I didn’t follow up.
Thanks to a recent Facebook post by thepennyhoarder.com, I clicked through and reactivated my account. It had lost touch with my email account somehow. Soon refunds will start magically appearing in my bank account again. The service is free.