There is this phenomena in direct marketing called “the ugly postcard.”
In test after test, when a plain, “un-designed” postcard was tested against a slick, shiny postcard, the ugly postcard out-performed the shiny one hands-down.
I bet you’re saying, “Yeah! Explain that, Miss Fancy Pants Designer!”
Well, maybe you’re not saying that. But I’ll explain anyway.
Did you read the post about giant wristwatches? Aesthetics (visual appearance) is not so much about how beautiful something is. It’s about the response that is elicited. (You might want to read that sentence again).
A lowbrow design has power equal to a high-end design in influencing perception.
That means an ugly design can elicit responses such as “easy to work with,” “affordable,” or “honest.” Or it could be part of your brand (like Craigslist’s look). Or it could just be that it stands out from all the shiny, “smart-looking” marketing competing for attention. 
So what’s an aspiring entrepreneur to do? Ugly or slick?
First, don’t go all ugly on yourself unless that is part of your message and your brand.
This concept is more powerful in direct marketing efforts, but much harder to pull off as a brand message.
If you’re sending a postcard or a sales letter, try a plain, undesigned look and see what kind of results you get.
Good marketing hinges on testing. So be bold and try different things.