I guess that depends on their view of WYSIWYG (What You See Is What You Get) editors. Most of the time if you view the source of a page that was created with such a program there will be a meta tag in the head section that says 'creator="Frontpage 4.0"' or something similar.
Sometimes you can recognize the code created by these programs by the absence of certain things. Most of them do not create a DOCTYPE tag. This tag is always the first line of an HTML file. It isn't required to have one, but it can help. For a good article on the DOCTYPE tag, you might check out
Fix Your Site With the Right DOCTYPE! at
http://www.alistapart.com/articles/doctype/.
A List Apart, where this article is located, has many helpful resources for web designers.
People may get the impression that a WYSIWYG editor was used simply because the HTML code is not structured well, and it may be difficult to grasp the intended structure of the page. Often this is simply becuase the author of the page is still learning about HTML. I learned HTML primarily by looking at the source code of other pages. You write code the way you learn it.
As with anything, the more you learn, the better you get.
Best Regards,
Narasinha