Most of these sites have FAQ pages for people who are, naturally anxious about dealing with money over the Internet, or are suspicious of the companies' motive... Here is an example FAQ, take from Spedia.net, but they are all the same anyway...

The important parts are in color!

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F.A.Q:

* Do I need to buy anything?

 No, you do not. Spedia membership is absolutely free. We will be
rewarding you for using Spedia every month by sending you a check.

* Who can participate?

 Everybody can enroll in our services. Spedia welcomes all Internet
surfers including International surfers. Spedia provides payment services in US dollars to all Spedia Members.

* What are the ways to make money with Spedia?

 You can make money in 6 different ways with Spedia:

-Spedia Bar - Surf the net and have the Spedia bar active on your
desktop. Go to your favorite web sites or visit our advertisers' sites if you're interested in the offers. To see a demo of the Spedia Bar, click here.

-Instant Cash - You can make over $150 in just one hour by signing up for programs. There are over 60 programs to choose from. In addition to the points you will receive from Spedia for signing up, you will take advantage of the benefits those programs offer you.

-Spedia Games - You can play games and make money while you play. It is free and fun. We have over 20 games to choose from.
Shop Online - Visit our shopping partners for special offerings and
promotions. You will be entered in a drawing to win our weekly
sweepstakes.

-Receive Emails - You can make 5-10 points for each email you receive from our advertisers. You can unsubscribe at any time. Your privacy is fully protected.

-Refer Your Friends - There are 5 levels of referralscompensation
structure for surfing is 10%, 5%, 5%, 5%, 5% for a total of 5 levels! To read our anti-spam policy click here.

* Do I have to click on banners?

 NO! Spedia does not reward you for clicking on banners. You
accumulate points when you have the SpediaBar active on your desktop and browse the Internet. Please, visit our advertisers ONLY if you are interested in their services and offerings.

* How does Spedia generate its revenues?
 
 Spedia sells advertising space to advertisers and sponsors and
distributes most of the revenues to our members.

* What kind of ads do you display?

 Our ad server will manage the placement of all ad banners. Spedia has a strict policy related to ad banners and other advertising materials, so you don't have to worry about indecent postings. You and your visitors (if you have a web site) will not get disappointed or frustrated with the ad materials. To learn more about our ad policy, please click here.