[reclino]

I think all your comments are valid
However, attempting to regulate or codify the used parts market is going to end in disappointment, frustration, or both. Some people here refuse to follow the simple rule of list a price, and refuse to when reminded that this is a rule. I have also missed out on some items here, and wondered who the heck responded faster...
In my view the seller has the part, and can decide who they want to sell to, and for how much, and for what reason, maybe a local buyer wasn't first to respond, but did offer to swing by and pick the item up, making the sale easier for the seller.
Buying and selling stuff can be stressful, I keep coming back here to reduce my level of stress, not add to it. Sometimes I score some really useful parts here at a good price.