They want the tags used properly before they'll accurately display your Web page. Of course, wading through pages of HTML code looking for errors may take more time and expertise than you posses. If so, use an HTML validation tool like HTML Toolbox. It looks like an old science experiment. Ok, so maybe you have updated your content since the year 1215, but you'd be surprised at how outdated some of the stuff on the Web really is.
Visitors return to sites that are continually updated with fresh and interesting content.
Be honest now. If so, you're a distinct minority. You'll get a lot more traffic if you do the work yourself when you design your site. Avoid browser-specific tags and other problems that limit your site's appeal with HTML Toolbox . They got to the good part of War and Peace.