You promote your site, if is not well designed, you are promoting a bad image. Now a professional looking site does not have to be filled with the latest technology, graphics and Java applets which take up space and time to download, however it does need to take account of a few website design aspects overlooked by many homebuilt sites. The most common mistake made here is not optimizing the graphics, and any image or music over 30KB is probably too large. The site must be easy to navigate so that a visitor can find what they are looking for with one or two clicks. What may look great on one browser may look unprofessional on another.
Websites also look different on screens with different resolutions.
A website designed on a 640x480 screen will look different on a 1024x768 screen. Lastly and probably most importantly, the content of the site must be good. Not only must it be good, but also it must offer a benefit to the visitor. The content must be interesting enough to either make the potential customer buy on the spot, with the use of compelling headlines or banner ads, or it must give them a reason to return. If you are maintaining your own website, keep it simple.