There are just a few rules to follow when you decide to survey your customers. It has been determined that for the best results the survey respondents should be:

Independent – people that have no ties to your organization and either are interested in helping you stay in business because they like your company or have a problem with your company and for various reasons would like to make you aware of that problem.

Diverse – people of both genders, all age groups, all/any ethnic groups, any religious persuasion, any sexual orientation etc.

Decentralized – people that are not restricted by location, job function, status, industry, etc.

…and you should have an effective method for aggregating the information.