For this example, let's just lump me in as a "vendor" for this little topic. I am NOT for it, and personally choose to refrain from solicitation here simply because I feel this forum is more for hobbyist-to-hobbyist interaction. I, ...like several others here, are hobbyists too and own/drive our Model-As on tour. That is why we are here. Therefore we are participating here as a hobbyist first but with the experience of a professional. Not all vendors own a Model-A (restored or otherwise).
Why I feel this becomes a slippery slope is when a site becomes full of business ads from vendors promoting their product, to me it is much like the annoying computer pop-up ads we all despise. How do you regulate who is posting too many promotional ads? Does it become a competition amongst vendors for post content?
Let me site an example. Since James Rogers and I are very close friends --yet competitors in the engine business, I am going to use him as an example because I know he won't care. Suppose he writes a post showing how he installs valves in a Model-A block, and then offers a promotional sale ($$ discount for 30 days). Next I perceive this to be a business advantage,and since I use a different machine to do my valve work, I post another thread showing my methods, showcasing my machines, and talking about why I perceive my method/machine is better. Now you have Rich Fallucca (another friend!) reading both of these posts and now maybe he feels obligated to interject his thoughts & processes to keep market share over us two "characters"!

From there the Gulbankians deserve the right to post, along with a dozen others. Soon the posts turn into a perceived competition for marketshare. Is that really what we want here?
One thing to remember is a forum is many things to many people. I don't have the spare time to devote like I once did and many others come here with limited time to browse/lurk. Like pointed out in another recent thread, many use this forum as a way/game to learn about troubleshooting and repairing their Model-A, and they read topics to see if their thoughts on the process are the same as others who have first-hand experience with that task. This is great for the hobby as it promotes 'restoration' knowledge and varied aspects on driving the Model-A. This knowledge and confidence the forum reader gets here is likely shared when a fellow hobbyist has a breakdown on tour, or needs a helping hand in their garage. A vendor will always have an answer why his 'widget' or 'service' has an advantage over is competitor. It really would not solve the "poor quality" issue so often spoken about here. That is solved by customers and their control over their wallet. I find most speak one way but choose another when spending their $$. If that weren't true, then the vendor would go out of business selling the inferior products.
Again, my view is that is likely more important to a reader than knowing what item(s) a vendor has for sale or what new item they have on the market.