Do not use HTML tags. For example:

a, b, i, ul, ol, li, h1, h2, h3, h4, strong, em, table, tr, td, th, p, br, div, span, href, img, style, src, width, height, border, etc.

Do not use "less than", "greater than", "equals", [square brackets] or {curly brackets}:

<, >, =, [this], or {this}

Anything on these lists will be automatically stripped out of the ad. And when that happens? You ad will be left looking like dog poo because I'm not taking all of it out, just enough to render it useless.

In addition: Don't use strings of asterisks or tilde's or dashes or dots as an artistic way of separating paragraphs. Doing this forces line length and breaks both the site and the RSS feed. These symbols in your ad will cause it to bomb out of the submission process with an error message.