The design and use of surveys is a big subject - much bigger than the card on the table at Pizza Hut. A Google search on "survey design" brough up almost 4 million "hits."
It's a serious business among researchers, who have developed methods to maximize confidence levels - and minimize the effect Steel described.
But although a well crafted and administered survey can indeed be objective evidence, but its usefulness is limited. For customer satisfaction I more recommend the one-on-one with sales people - surveys don't explain why people select the answer they do, and most don't bother to fill in details. The information in surveys is often not very actionable and sometimes it data is too late to act on. Then, if you do act on it a follow up survey may, or may not reflect an impact. Its responses may have been entered for other reasons.
It's a serious business among researchers, who have developed methods to maximize confidence levels - and minimize the effect Steel described.
But although a well crafted and administered survey can indeed be objective evidence, but its usefulness is limited. For customer satisfaction I more recommend the one-on-one with sales people - surveys don't explain why people select the answer they do, and most don't bother to fill in details. The information in surveys is often not very actionable and sometimes it data is too late to act on. Then, if you do act on it a follow up survey may, or may not reflect an impact. Its responses may have been entered for other reasons.
Saying, what are you trying to suggest by the word objective? Like BevD suggested in her post, it can go many different ways.