Well.... Let's flip this around a bit. If you were shopping for some widget, but didn't know too much about said widget, wouldn't you be happy if someone who did know about them chimed in while you were shopping? It leaves a sour taste when you buy something, only to discover you overpaid. Sure the seller is happy, but the buyer feels ripped off.
The problem is there's never a happy medium, no easy way to say "You offer X, I offer Z, lets compromise on Y." Especially in a market that fluctuates as much as the used Tesla market, there's too many variables.
I don't think it's reasonable to equate a car which sells from $50K to $90K is equivalent to some "widget", nor (as
@yousexy already noted) is it likely that people coming here to look for a Tesla don't know much about "said widget". I would really think anyone even considering the purchase of a used car from this forum would also check other sources and have a clue what they're buying... if they didn't, they would consider this extremely risky and would be going to a Tesla store and asking for
their used cars.
Even if you assume that a buyer is ignorant, which I don't, simply seeing several cars here on TMC offered at different prices will give them a clear look at the range of prices available. That, plus the Tesla site itself and its new/used inventory always available online, are already significant sources of price information. To go even further, an interested-but-ignorant buyer could just start another thread linking to the for-sale thread and asking for advice on it. There's no shortage of resources for the buyer to become educated on current pricing plus every other variable they may care about.
And lastly,
of course there's a happy medium! I didn't sell for my asking price, nor even close to it, but I sold the car quickly because it became clear to potential buyers that my car was in great shape, I was making every possible effort to be transparent (I even supplied a spreadsheet with nine other cars against which to compare mine), and I was perfectly willing to listen to, and address, any price negotiation. It was as simple as what you say can't be done: I asked X, they offered Z, we compromised on Y.
And
none of that really benefits from people trolling for-sale threads and being snarky about whatever they think is right or proper pricing. Really, it's no one's business except for an interested buyer and the seller.