How to do a rock survey?

Hi Medhat! Last time that i did a survey I reached 300 valuable opinions. Instead of asking for completing it for free, i created a small ebook about marketing (the product was on marketing category too). Therefor, the ones that completed the survey received the free ebook. Also this was important because the opinion where more valuable than random people that just want to help but are not actually posible client/users. By the way promoted the survey+ebook on facebook and reddit groups.