You absolutely don't want to put the site owners in a spot where they have any responsibility for determinations of ratings, or suitability to post.   Once I have to recommend to Ed that XYZ company be listed, and he has to make a determination that 2 other people like them and 3 don't.. you are making him an endorser.   That has legal and business implications.

I don't think a forum is the way to handle it.  I think a user will have to be able to add a company to a database, and in the process, have a set of checkboxes for all service/product categories that apply.   And then any user out here could search for service product categories to find companies that have them, and they can add comments (good or bad) about their experience with that company.

Like all systems, there is the potential for abuse by companies posting comments under various names, etc... but I don't know how you avoid that with admin taking too much of an active roll in the process.