I'm not a fan of customer satisfaction surveys, in the past my highest return rate was about 15% and those that responded were the ones that usually had an axe to grind.
As to the sample size aspect, I would suggest that all customers be addressed, this is not an area where sampling would be effective. There would be too much bias in such a system that the results would not give you a true picture of customer satisfaction.
I would like to hear from other forum members if they have had positive results with customer satisfaction surveys.
My concerns are as follows:
Who in the customer structure do you send the survey? Managers, Quality, Engineering, Floor personnel?????
Does the person you send it to even know your product line?
Does the person you are sending it to have 20 similar requests from other suppliers?
Did the person you are sending it to have a fight with thier spouse last night and is in a bad mood?
I could go on with the variables but there are much better methods of determining customer satisfaction. Be creative and make it work for your organization, the methodology is up to you!
(PPM/Delivery/Cost/Responsiveness/Audit Results/Repeat Business/New Business/etc...)