I get these emails from a survey site. I used to do a lot of them, but recently the "promised reward amount" is now basically a lie to try and get more responses.
In the last few surveys I've completed, I will spend 15-20 minutes answering fairly comprehensive questions. At a certain point the survey will inform me that "thanks anyways, but you aren't eligible for the entire survey. Your account will be awarded partial reward credit". There is no indication why I'm not eligible, and a $4 survey will give you around 10 cents. By doing this repeatedly it has negatively influenced my opinion of the represented brands in the questionnaires, despite the blame likely falling on the E-Rewards site.