It all depends what you are selling. I feel good design inspires confidence. But like pete says it really depends on the item.
For instance if I'm looking for a cheap toner cartridge I can't care less about the design, I just want a good price. If I am buying a 3 grand plasma tv, I wouldn't use a site that looked mickey mouse, unless it was a well known business.
Ultimately, everyone who is serious should have a well designed, easy to navigate and functional website. Having your own template/skin custom designed costs anything between £200 and £1000. It is money well spent.
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Didley Squat now in stock. Going to be a FAST mover!