I don't think there was ever any intent to just knock somebody's model A.

When something is for sale I don't see any problem in discussing what is right, or what is not as far as a "correct" model a, or discussing obvious mechanical or safety issues that are in need of repair, correcting, adjusting or whatever. That in itself is constructive in my opinion and helps us all become better informed whether we are buying or selling a model A and might even help us identify things to make our car better.
There were also obvious misrepresentations in the ad on what the seller thought of the details. I suspect most of this was out of ignorance but he also naturally wants to talk up the merits for a sale that will benefit him (understandable). But if you're going to sell a car you better have the facts straight and be ready for potential sellers to speak their mind on what THEY think the value is to THEM. If the buyer and seller don't agree and cant convince each other? fine. They buyer will look elsewhere and the seller will have to try harder with someone else. Maybe both will become more informed in the process.
If you are afraid of getting butt hurt about what others say your model A is, or what you or a family member has done to it, then keep it in your garage and don't show it or sell it.
Personally I enjoy comments and feedback on my car, good or bad. Sometimes it helps me address issues, and other times if it doesn't affect safety or reliability, and I'm happy with the way it looks - I'll just dismiss the comment because what matters to ME is the most important part.
Just to reiterate....*I want to emphasize ESPECIALLY when something is for sale you can expect critical remarks regarding said car.* Its not like just walking up to someone and saying this, this, and this, is all wrong. That's worn and ugly, etc. Sure that would be rude and uncalled for unless the person was really asking for an honest opinion and critical remarks.