Picture a website with cutting-edge design, cool graphics, interactive bells and whistles, and sophisticated e-commerce infrastructure. Compare that with a stark website with no graphics or cool technology just web copy on a plain light background. Which of the two websites is more likely to sell a product or service?
You cannot factor it down to something as vague as that. It will depend on many MANY more factors. Whats the product being sold? What's the audience? Even down to the grammar on the page. WAY too many other factors.
Whats the product being sold? --- Does it really matter ? Construction chemicals to Hypnosis Tecnique Books What's the audience? --- Mixed
More than the design, I think it would depend on what you are selling, how the product is portrayed on the site, user friendliness of the site and the target audience. Since you have mentioned that the target audience are mixed I think the design should be simple yet attractive.