You're focusing on the device on which you are taking the surveys. I really don't think it's all that complicated. It's not anything on your device that cuts off the surveys, obvious to me that e-rewards has a set limit on the number of surveys that can be taken by any account in one sitting (or some time period), and they simply "cut you off" from further surveys until that period expires. Not a matter of a "fingerprint" left on your device, or a cookie, they are controlling it from your logged in account on their side. When it kicks in, you can click on current or old survey links until you're blue in the face, generally it "ain't goin' happen". And they obviously are not goin' communicate as to what their specific policy is...