I only do the ones that appear on the top of my screen on the "surveys" section of earning free credits. Usually has a brief description like "product survey" or "opinion survey" with credits from 120-150 for the majority of them. Usually asks 1 or 2 qualifying questions (sometimes as easy as how many nickels in a buck or what color is a banana".
They never require a credit card, money, or anything invasive. Those I won't do.