Why not only allow Gold Members to post in the classifieds?
There are several reasons.
Disclaimer: Nothing I say below is directed at anyone in particular
First of all --- lets assume its your for sale thread. How would you like me posting about how the part your selling isn't worth what your asking? Or that I can get a better deal by going somewhere else like ebay or CL? How about I post that your part is crappy and I'm selling the same part for less? How about if I just don't like you and post that your a douchebag to do business with? (whether true or not)
Those also are comments. Negative comments. And if I allow positive comments, then I have allow negative ones. And how do you respond? Now we have an argument over a part because you take issue with my criticizing your ad or trying to steal your sale.
Not to mention -- every comment pushes the thread to the top of the new posts list ahead of other ads. So that ad stays at the top.
OK, so someone is selling a part for more then its worth (in your opinion) -- So what? Let him. Its worth what someone will pay for it, not what YOU think its worth.
All those comment I described above also clutter up the ad, so someone looking to buy has to read through a bunch of comments about how great the part looks, or how crappy it is or how high priced it is, or whatever, just to get all the info.
Care to show me a site that allows such comments? eBay? Craigslist? Nope. Why? Because it turns things into a mess.
SO as you can see, this isn't about censorship, this is about keeping ads clean and easy to deal with. If I allowed comments we would have for sale ads reported all the time and would have to moderate things all that much more.
I know, right now your saying to yourself "Joey has really thought this out" or "Gee, I didn't think of that" Yes, after running this site and others for more then 12 years, I've learned a few things...
SO, in the end, its really pretty simple. If you have a comment that's really important, send it in a pm to the seller.