I'll toss my opinion in...
I just now saw this thread and voted for no limit.
We'll say, hypothetically of course, that there is a member who has no interest in contributing to the community here other than offering parts for sale and trying to make money.
I occasionally browse the parts for sale section, just to see if there's anything for sale that I need or want. Part of my browsing there isn't even about looking for anything to buy, I just enjoy looking at what people are selling.
If someone has something they're looking to sell, I don't want them to be unable to post it for sale here just because they don't have the requisite post count. It could be something I want, but don't necessarily need and wouldn't start a WTB thread for.
I don't make a habit of window shopping the for sale sections of other forums (mostly because I don't go to other bike forums, because compared to the DMF they're not very good), and I only check ebay for specific parts that I actually need.
So I say let them post their ads.
If they don't post the info you're looking for, back out of their thread and move along to the next one.
Or, alternately, give them a hard time about not posting a thorough description and not being good about answering questions and not posting pictures of their parts. Personally, I find reading that sort of thing very amusing and get a great deal of pleasure from it.
But don't prevent anyone from posting things they have for sale, because we might miss out on some good stuff.
But that's just my opinion, so feel free to ignore it if your differs. My vote's in the ballot box.