Just to clarify, the templates you are referring to contain required information that should be present on ALL threads tendering goods/services within the marketplace section.
Ok, I've tried to put in a HTML template, wont work.
Is there any mod that could allow HTML in posts for sellers, then they could design there own templates.
HTML is disabled (always has been). Enabling it would open us to a world of potential security threats (vBulletin themselves also recommend it be disabled). BB Code is enabled though, which controls all the style elements of posts.
They can design their own templates now, they have the freedom of colours, sizes, font types and so forth. What else did you have in mind?