Google Opinion Rewards are offering you Google Play credits in return for your opinions. Earn credits by completing quick surveys. Download their app and register. They will send you surveys about once a week.
To receive your free Google Play credit, click 'get freebie' and download the Google Opinion Rewards app onto your Android device. You will need to register in-app by giving some details about yourself. They'll then send you quick surveys such as "Which logo is the best?", around once a week.
You can receive up to £1 in credits and spend them on Google Play.