A few suggestions: 1. Hire someone with experience on experimental psychology, I mean, by trade. Not necessarily a PhD but at least with some experience and has knowledge of the textbook experiment errors. Just one of those would help the design a long way. 2. Throw in some free analytics tools/result for the organization behind the survey. As you mentioned, restaurant owners and politicians might just want to run the survey for some straightforward result, well, not all surveys have straightforward result, even when designed well. Some analytics/visualization tool, e.g., manyeyes from IBM, doesn't really take a lot of dev time but would be quite impressive in the eyes of your customers (i.e., the politicians or restaurant owners).
Best of luck, Alex