MoBee - Make Money Mystery Shopping
The Mobee app lets you make money while you shop by becoming a mystery shopper. There are a ton of secret shopper offers that aren't on the up-and-up, so you may be skeptical -- but users are big fans of the service.
You need to create an account and choose a business that you want to secret shop. You will get a mission at a retailer or restaurant that you can then complete to earn points.
There are a variety of locations and businesses you can earn money at, but you may have the best luck in a larger city. You can redeem points for gift cards, merchandise or cash.