It'll never work.
The guide will be as thick as the old school yellow pages and no-one in their right mind will read it if their heart is set on a purchase that tickles their fancy. Then, buyers will get the peevs if they make a bum purchase and get asked/told post bum purchase; "did you read the 400 page buyers guide". That'll open up a whole heap of manure thats not needed.
Why dont you run a test phase - in a certain section of the classifieds only? Maybe run the comments in the, gosh I dunno, ... components section first. If it works and isnt taken out of context, then roll it out to other sections of the classifieds like the bikes or whatever is the fastest moving department.
A simple classifieds comments section will be better and certainly easier to manage from the local hub police. You guys can then step in as bossmode if it gets out of hand - which I cant see happening much after the first month anyway as the chancers will get taken to the cleaners straight off the bat and it will set a precident going forward. Its much easier from a mod workload point of view imo