Many people purchase items online and never realize that they provided someone a commission for the sale. We've all gotten the annoying emails that want us to click on a link and most of us realize someone is getting a commission for bothering us. However, any website that you visit with links to a store likely gets a commission for that link.
Just today I was researching solar panels for my house. The first page that came up had some good information and a lot of links. I could tell when I clicked on the links that most of the links were to earn commissions. Does this make the site less useful? Maybe, and maybe not. Another example of useful sites that get commissions are the price-comparison or coupon-finding websites. I've used these sites a lot, and often I feel they deserve the commissions.
Some people are out to send spam emails or set up useless sites just to get clicks. Some of these people are very wealthy, and you can be sure they keep every dime of their commissions. Some sites are meant to appear informational and are often very useful. These sites use commissions to pay for professional staff who write reviews and create the content that brings you to them.
Parish Funding and Innovative School Funding fall into another category of websites. These sites offer rewards for purchases. Some of these sites make big money on getting your personal information, which is worth more to them than the commissions on your purchases. Parish Funding and Innovative School Funding are websites specifically created to raise funds for non-profit organizations, and they don't collect any personal information. Their theory is to get as many sites up as possible for free with a low percentage taken from commissions offered by retailers.
You're going to spend money online anyhow, so you choose what kind of company gets the commissions for your purchases.