I think it boils down to how we see the membership. Are we mates, colleagues or just a resource.
I was interested to read about a mates rate being offered when there is hidden pricing - something is up for a certain price but the seller will sell to certain folk at a lower price. I hate haggling and only make an offer when one is invited. I would not be aware such a price was available.
Naturally, anyone can sell their own stuff at whatever price they like. Like I said, I have a mental list of people (which this thread is expanding) to whom I wouldn't want to sell, because I feel their subsequent sale is again my own view of this place. As with sellers, that is my perogative.