Before I go on…  If you have no idea what a browser cookie is I would suggest that you take a look at The Unofficial Cookie FAQ or browse on over to the Wikipedia article on the HTTP cookie.

Some people and anti-spyware software would have you believe that all browser cookies are bad (especially “tracking cookies”.)  When it comes to paid survey, incentive, GPT, and PTS sites (hereafter referred to as the “incentive site” for the sake of simplicity) cookies are your very best friend.

How do incentivized offers track?  Most use a combination of tracking cookies, the single pixel gif, a sub-id containing your site membership information, and your unique ip address.

1. When you click on an offer/survey the incentive site’s software will note your click.
2. You then will be sent to the offer’s url with a sub-id usually containing your incentive site user name appended to the end of the url.  Though is may seem instantaneous and direct on pretty much any connection other than dial-up, your browser is actually being sent on a wild goose chase of many different urls to get to your final destination (incentive sites use sponsor (or “CPA” / “affiliate”) networks as a source of their offers – those sponsor networks usually get their offers from other bigger sponsor networks.)  The only way to properly make sure that everyone the should be paid for your “lead” will be paid is to send you through a daisy-chain of successive URLs (each noting and crediting themselves your lead.)
3. Ok, you arrive at the survey/offer.  You fill out information, make a purchase, or perform whatever “action” is required to generate credit.  This is where the tracking cookie and single pixel gif come into play.  Once the action is performed then you are usually sent to a confirmation page that will place a cookie on your computer eventually reporting to the original incentive site that you have indeed completed the required action for credit.
4. Another reporting method is the mysterious single pixel gif.  This is a uniquely named image (picture) file that is so small (1 pixel by 1 pixel) that it is invisible to you that is placed on the confirmation page.  The gif is uniquely named so that it specifically and only refers to you specifically.  The offer’s web server knows that you have completed an action when a request is made to “show” that one pixel gif (known as the gif “firing” in the industry.)
5. If the offer site notices that you already have a cookie on your system from a previous session at that site (indicating that you are NOT a “unique lead”) then it may internally note this, allow you to continue, though ultimately report to the incentive site that you are not qualified for the incentive (ouch!)  The same goes for if you are recognized by your ip address or entered information such as your name, email address, etc.)  Your ip address also plays a part in identifying if your are within the required geographic location for that offer.
6. Once you are done viewing/completing the survey/offer, close browser window of leave the site, and end up back on the original incentive site then the tracking cookie reports that you have or have not qualified for your incentive.

Most all of the offers are on the up-and-up.  But, always keep your guard up and always read the fine print!  A very few offers come with surprises that may turn out to be a headache for the unwary.  In my online travels I have run across offers that seem too good to be true until you read the fine print.

Here are a few snags to look out for:

• Offers that state in the fine print that you are signing up for some sort of service (usually voice mail, or the like) that will be billed on your telephone bill (yes, they CAN do this – even if you give them the wrong number! — they'll look you up and "correct" your obvious error (smile))   This practice is called "cramming" you phone bill (though in most cases YOU are actually signing up to be billed if you read the fine print.)  You can read a bit more on cramming here (FCC link.)  My advice is to always read the fine print and call your telephone service provider (AT&T, etc.) to "Block Third Party Billing" (beforehand.)
   

• Offers that are "free trials" that charge you some nominal fee (like a buck or two) during the trial period but if you don't cancel within the trial period you will be charged full price (usually a much greater cost) or that your credit card will be billed on a recurring basis until you cancel (Argh!)  Again, read the fine print!  Some free trial offers may make it difficult, laborious, or impossible to cancel.  Watch out!  Free/low cost trial offers that turn out to be extremely difficult to cancel (some customer service numbers run perpetually busy, or put you on hold for hours, etc.   …or some web site based cancellation links just lead you to an "error".)  Read the fine print.  Save all copies of emails you receive.  Print out any specifics such as login info, account numbers, offer agreements and terms of service (TOS), etc. that are presented on the screen.  Print and keep a hardcopy file of all confirmation screens and emails!
   

• Offers that ask for credit card or other private financial information without presenting you with a secure server.  In Internet Explorer, you will see a lock icon   in the Security Status bar.   The Security Status bar is located on the right side of the Address bar.  The certificate that is used to encrypt the connection also contains information about the identity of the website owner or organization. You can click the lock to view the identity of the website.  If you are being asked for any private financial information without them taking minimal precautions to protect that information (by using a secure connection) then move on – don't give them any information!
   

• Cell phone offers that have you enter your mobile phone number, wait for a text (sms) message containing a pin number or password, and then have you enter the number in back on the web site.  They will call this "confirmation".  Usually, what you actually are doing by confirming your pin number is giving them permission to add you to a subscription service that will bill your cell phone account some amount ($9.99, $15.99, $29.99!) on a regular basis until you cancel.  Always read the fine print!  Know what you are signing up for.  To avoid costly mistakes you may want to contact your mobile phone service provider beforehand to see if they offer some sort of subscription service blocking / 3rd party billing blocking service (beforehand.)