Your data is already being sold. Every time you click something on google, every time you allow a website to see your location, your data is stolen and sold. Why not get a cut of the profits? These apps and browser extensions will pay you 50-150 dollars a year for your data.
The majority of people do not utilize all of their bandwidth, leaving it to go to waste. With these apps you can sell that excess bandwidth at a rate of 20 cents a gigabyte. It's not the biggest payout, but after you set it up, you don't need to put any work into it.
Every year hundreds of billions of dollars are spent on advertising. You, the consumer, are the end product of those billions and yet you don't see a single penny of them. Why not get your fair slice of the pie? These extensions will help with that.
Many different apps will pay for pictures of your receipts. They then aggregate this data and use it to understand purchasing trends.